ISIS or her more ancient Egyptian name ASET, seems like two different deities if you take a closer look. When the worship of ISIS rose in Greek and Roman days, ASET had already been forgotten for hundreds of years, at this time only a small group of priests still knew how to read the hieroglyphs of the temple walls. The Greek and Roman way of superimposing their cultural values on Egyptian culture affected the interpretation of the original ASET, depriving her of her Egyptian origin and turning her into Roman deity. The most outstanding difference between them is in my opinion the fierceness of Aset which we can find in the myths, along with her role as a funerary deity. This is not so with Isis who is a much more benevolent and one-size-fits-all kind of a deity.
This image shows an almost schematic picture of how Aset merged with Isis.
To the far left she is shown with her original hieroglyph, the throne above her head.
In the middle she wears the horned solar disc combined with the throne, now she is being merged with Het-hert.
Finally she is pictured as the Great Mother in the shape of a cowheaded female
crowned with the horned solar disc and two plumes.
Origin
Isis, or Aset, as the original, ancient Egyptian name was, goes far back into history.I will here use the Kemetic original name of Aset instead of the Greek name Isis.
The Name of Aset
Aset, or Ay-see as it is believed to have been, is written with the hieroglyph for "throne" or "seat". This indicates that She was seen as the one Who supported the king and from which he rose. This was the case in early African cultures and is still to some degree today. So Aset can be taken to mean "The Seat/Throne" of the king. Thereby she was the King´s symbolical mother and as such of special significance to him, but in these early days she was not a great mother goddess whom everyone turned to.
Great of Heka
Aset is often called 'Great of Heka'. This stems from a myth in which Aset tricked the sungod Ra into telling her his secret name. In ancient Egypt words and writing were considered sacred, a gift of the gods. Therefore they were powerful and 'magic', whether uttered or written. He who knew the name of someone or something also knew the true meaning of the thing or the person and thus gained power over it. This is often the case with African religions even today. Read more about her different names and aspects.
Mortuary Deity
Aset and her sister Nebt-Het are often depicted on coffins in the form of two kites with outstretched wings, protecting the deceased on his bier. Aset is placed at the feet end and Nebt-Het at the head end. The connection with the kite might have been because the wail of the kite resembled the sound of weeping and mourning women. They were also depicted in anthropomorphic form, each with their hieroglyphic sign above their heads, and wings along their outstretched arms.
She is also seen in the Hall of Judgment standing protectively behind the throne of Wesir (Osiris), her sister Nebt-Het is also here by her side.
As the Mother of the king She is often seen standing behind Wesir or Pharaoh, supporting him with arms outstretched. There are also many depictions of her sucking Heru on Her lap or, as in a relief at Abydos, making offerings together with Heru to Wesir.
Myths
The most wellknown myth about Aset, is the story of how, when her husband Wesir was murdered by his brother Set and his body thrown into the Nile, she mourned and went out searching for his body, accompanied by her sister Nebt-Het. When, after many adventures, She finally found him, She managed to bring him back to life and beget his son Heru who would in time win the throne back from his uncle Set.
The myths also tell about how Aset hid Heru in the marshes of Chemmis and how She brought him up alone. There is also a story which tells about how Aset interferes when Heru is fighting Set, in order to help Her son regaining the throne of Egypt.
Late Version
At certain points in history the myths were 'edited' by the priesthood in efforts to strengthen a certain deity´s influence, and thereby themselves of course. The myth cycle of Isis, Osiris and Horus is known from the Old Kingdom, and it is hinted at in the Pyramid Texts, but it was heavily rewritten and added to by Plutharch (ca 46- ca 120).
Go Here to read these myths.
Historical Run-through
Aset in the Old Kingdom
Already during the Old Kingdom she was known from the Heliopolitan Creation Myth where she was the sister-spouse and mourner of Wesir (Gr: Osiris), sister of Nebt-Het (Gr: Nephtys) and Set, all of them children of Geb and Nut of the Heliopolitan Ennead. These two, Geb and Nut in their turn were the children of Shu and Tefnut , who were created by Atum , the Creator God. Further she was the mother of Heru (Gr: Horus),
the child and heir of Wesir (Osiris) whom she helped by her deeds to the throne of Egypt.
Read about Aset in the Ancient Texts.
Aset in the Middle Kingdom
In the Middle Kingdom her popularity rose among the common people, together with that of her husband ,Wesir (Osiris). This was an effect of the democratisation of funeral habits and the concept of the Afterlife.
In the Old Kingdom only kings could gain eternal life after death and therefore had their tombs inscribed with texts supporting their being born again, transformed into Osiris. During the 1st Intermediate other ideas and habits slowly took form, so that during the Middle Kingdom everyone who could afford, supplied either a wooden coffin inscribed with texts, or a roll of papyrus, which would assure his entry into the realms of Osiris. During this time period Aset was not as often mentioned as in the Old Kingdom days, even though her cults are attested during the Middle Kingdom at Hierakonpolis, Edfu, Akhmim and Koptos. It seems though that already at this time people were drawn to Aset as a deity who was familiar with suffering, even though archaeology knows of few temples dedicated to her.
Read about Aset in the Ancient Texts.
Aset in the New Kingdom
After the Second Intermediate, during the New Kingdom, references to Aset are more frequent, now in the Hall of Judgment, accompanying her husband or sitting in the council of those who judge the deceased. There are those who ascribe Aset´ part in these judgment to the heightened power of women in the royal family of the 18th Dynasty. In the 19th Dynasty she was at least worshipped at Gebtu north of Luxor and also in the southern areas of Nubia there were temples built to her during the reign of Ramesses II. She was here even called the Mistress of Nubia.
Read about Aset in the Ancient Texts.
Aset in the Late Period
Her cult continued to develop throughout the New Kingdom, and into the Late period. During this time she incorporated most of the traits of the other great goddesses and also some gods. It was probably easy for people to identify with her, especially for women, because of her sufferings as a widow and lonely mother. She was also greatly worshipped for her healing and protective powers and love spells and amulets (the tyet knot) connected to Aset were frequently used. Her popularity grew and endured longer than any other Egyptian goddess into the Greek and Roman days when she became interpreted according to their cultural values and religious viewpoints.
The last cult center was the temple of Isis built and added to by several rulers from the 30th Dynasty to the late Roman period, ca 300 A.D, held its own until it was orderd closed by the emperor Justinianus in ca 535 A.D.
See the Sacred Island of Philae.

A note about HEKA, MAGIC and the power of WORDS:
The ancient Egyptian word heka could be translated as "magic". It would be more correct to call it Life Force in Action. In our modern day Western society the word magic has other connotations than the ancient Egyptians attached to the concept of heka. The word was neutral in itself and could be used to direct oneself to the centerpoint of cult and of creation, for maintaining the Cosmic Order and Balance (see Ma´at). In other words, it was no more and no less a form of ritualized prayer. It could be used to refer to texts which were written or spoken.
Words in themselves were regarded as divine by the ancient Egyptians, and were to be treated with great respect. Weret-Hekau, Great of Magic, was one of the titles of Aset, as in myth she managed to trick Ra into revealing his secret name to her. The same title was also used for Sekhmet. To know the name of something meant to have power over it.
Heka was not only particular to the deity who acted from and with it, humans too have life force and can of course use heka to come into contact with the divine. The ancients believed that with the help of heka they could influence the world of the gods.
As heka was used both in temple ritual and in more informal situations, one sees the possible reason of equating it for "magic". It had, however, nothing to do with evoking spirits or any supernatural phenomena. It was a way of addressing oneself to God.