|Two images of Nephthys, one from Wallis Budge (1904), the other a carved statue (Ѻ) figure.|
The birthdays of Nut’s five children, in the epagomenal days myth, are: #1 Wesir (Osiris), #2 Heru-wer (Horus the Elder), #3 Set, #4 Aset (Isis), and #5 Nebt-het (Nephthys). (Ѻ)(Ѻ)
Body parts goddess
Nephthys, in one dominant role sense of things, was generally known as the “Lady of the Body” or “Lady of the Body of the Gods”, which Budge (1904) summarizes as follows: 
“Nephthys always appears as the faithful sister and friend of Isis, and helps the widowed goddess to collect the scattered limbs of Osiris and to reconstitute his body. In the Pyramid Texts she appears as a friend of the deceased, and she maintains that character throughout every Recension of the Book of the Dead; indeed, she seems to perform for him what as a nature goddess she did for the gods in primeval times when she fashioned the ‘body’ of the ‘Company of the Gods’, and when she obtained the name Nebkhat ‘Lady of the body [of the Gods]’.”
This would seem to have something to do with astro-theology, in the sense of stars of constellations, e.g. Orion, as Nebkhat hieroglyph, namely the symbol: , which seems to be the dead Orion [horizontal (8PM) Orion constellation], seems to indicate, being the “body” or body parts of gods? Budge states that after during and after the Theban recension (1550BC) (see: recension theory), Nephthys main role became that as second assistant to Isis.
Osiris | Anubis
Osiris, according to the famous myth of Osiris, Isis, and Set, was said to have slept with Nephthys, then Set's wife, "by accident", therein creating the offspring of Anubis, per reason that he mistook Nephthys for his wife Isis, Nephthys' twin sister. This was the "act" that sparked the so-called "Passion of Osiris" tale, wherein Set first gets back at Osiris, for sleeping with his wife, by trapping in a chest, via ruse, during a dinner party, and then trowing the sealed chest into the Nile. Isis recovers the chest. Set then chops the body of Osiris into 14 pieces, scattering the pieces around the land. Isis, with the help of Thoth, finds the scattered pieces, makes a mummy out of them, and, with the combined help or power of Nephthys (and Thoth), resurrects (see: death and resurrection of Osiris) or brings back to life Osiris, from the dead, for a moment of time, long enough to procreate Horus. Horus then is born and avenges his father, by killing Set, therein restoring balance to Egypt.
The following are related quotes:
“Nephthys, although a goddess of death, was associated with the coming into existence of the life which springs from death, and that she was, like Isis, a female counterpart of Amsu, the ithyphallic god.”— Wallis Budge (1904), The Gods of Egypt, Volume Two (pg. 258)
“In the original resurrection of Osiris story, the Egyptian corn god Osiris who was shucked apart into 14 pieces [see: Orion]. Each piece was then scattered about the land and, as legend has it, wherever a piece landed a temple grew. Later these pieces were collected and put back together into the form of a mummy. To reincarnate this mummy, two special birds, Isis or Stela Maris (star of the sea) and her sister Nephthys, had to hover over the inanimate body so to impart spirit into it. Osiris was the world's first mummy. In the Christian version, Mary (Isis) and an Angel (Nephthys) had to hover over the body of Jesus (Osiris) to resurrect him, following his crucifixion (a reenactment of the shucking of Osiris into pieces).”— Libb Thims (2010), Hmolpedia forum post, Nov 17 (Ѻ)
1. Jordan, Michael. (1993). Encyclopedia of Gods: Over 2,500 Deities of the World (pg. 181). Facts on File, Inc.
2. Budge, Wallis. (1904). The Gods of the Egyptians, Volume One (§XV: Set and Nephthys, pgs. 441-60; §§:Nephthys, pgs. 254-60; Body of the Gods, pg. 255; Nephthys, 54+ pgs). Dover, 1969.
● Nephthys – Wikipedia.