The Goddess Isis was also known to the Sumerians as Tiamat, the Serpent of Chaos, the Ancient One, mother of the gods and all abominations of chaos. The Egyptian god Set was originally a female deity and was identified with Isis. Set is a god of the desert, storms, and foreigners in ancient Egyptian religion.
In later myths he is also the god of darkness, and chaos. Hence, the connection with the Sumerian Tiamat, the Serpent of Chaos, the Ancient One, mother of the gods and all abominations and Isis who we also know as Set, the god of darkness, and chaos.
Here is an excerpt from the book, "Psychology of the Unconscious: A Study of the Transformations and Symbolisms," by Carl Gustav Jung and Beatrice M. Hinkle:
"Isis, the mother of god, played an evil trick on the sun-god with the poisonous snake; also Isis behaved treacherously toward her son Horus in Plutarch's tradition. That is, Horus vanquished the evil Typhon, who murdered Osiris treacherously (terrible mother= Typhon). Isis, however, set him free again. Horus thereupon rebelled, laid hands on his mother and tore the regal ornaments from her head, whereupon Hermes gave her a cow's head. Then Horus conquered Typhon a second time. Typhon, in the Greek legend, is a monstrous dragon."
In the bible scholars often associate the dragon with the devil and we find Isis had morphed into Typhoon which means "terrible mother" also associated with the dragon. The Sumerian Tiamat who is the Serpent of Chaos could be to some the equivalent what they may call the Devil and this would be where we later would get the Egyptian Set connection to Goddess Isis. They all did terrible things and are associated with serpents, darkness and chaos.
Isis, the Dark Goddess was also often depicted carrying a phallic object which identifies the male emblem with its solar origin as symbol of the Sun. Therefor, she carries the sun under he veil for she is the the Great Mother to the Son of the Sun, Horus who she also nurses on her breast for she is the Moon Goddess or the Goddess of darkness, and chaos.
The name Isis means "Throne" or "She of the Throne." Her headdress is frequently shown with a a vulture resting on top of her head such as in the picture to the above left and in Egypt she was frequently called Man, and her totem there was a vulture. Below is the definition of vulture's feeding habits from wikipedia
Vultures seldom attack healthy animals, but may kill the wounded or sick. When a carcass has too thick a hide for its beak to open, it waits for a larger scavenger to eat first. Vast numbers have been seen upon battlefields. They gorge themselves when prey is abundant, until their crop bulges, and sit, sleepy or half torpid, to digest their food. They do not carry food to their young in their claws, but disgorge it from the crop. These birds are of great value as scavengers, especially in hot regions. Vulture stomach acid is exceptionally corrosive, allowing them to safely digest putrid carcasses infected with Botulinum toxin, hog cholera, and anthrax bacteria that would be lethal to other scavengers. New World vultures often vomit when threatened or approached. Contrary to some accounts, they don't 'projectile vomit' on their attacker as a deliberate defense, but it does lighten their stomach load to make take-off easier, and the vomited meal residue may distract a predator, allowing the bird to escape. New World vultures also urinate straight down their legs; the uric acid kills bacteria accumulated from walking through carcasses, and also acts as evaporative cooling.
This is why you see the vulture as the headdress of Isis. Let us just say that she has a very tough and important job to do in the ecosystem we know of as our lives. More so than many people will ever know before the vulture may kill the wounded or sick.
Isis became very powerful deity in the late Egyptian dynasties of the Greeks and the Romans because of her magical skills. You will find that Cleopatra had always appeared in public clothed in a robe sacred to Isis and magic her central role as the Goddess of the Darkness and Chaos we know of as our current world.