The witches Hecate really gets formed with Roman influence more so than Hellene influence. Modern Pagan's I think like to use Hellene, especially the story of Medea but to the Hellene's she was an outsider and use that to justify things and why Hekate was bad in that sense. But one also has to remember in that story Hekate is also more a High Priest to Artemis than an Actual goddess in her own right.
The Queen of Witches and dark magic and all really gets that label under Latin (Roman) lore more so than Hellene lore. Just as Hekate will change from a young woman to the older woman in imagery as well. A lot of that I believe in part due to the conflating with the Latin goddess Tri-Formus. Though to some degree it will also occur due to the conflating of Artemis-Hekate-Selene with Diana-Tri-Formus-Luna and the Sanctuary/temple at Nemi with Diana Nemorensis and the story of Orestes and Iphigenia. Which will also include the Rex Nemorensis, the blood slaying, the Temple of Artemis at Orthia, the Temple of Artemis at Brauron.
The Medea story though does tie into the Hekate influence somewhat into the Eleusinian Mysteries in that she is in the Samothrace area as it all ties into the Black Sea and Thracian influence. Unfortunately while the mysteries revolve around Demeter, Persephone and Hekate she does not participate as a member at all the sites where the mysteries are actually known to be performed. Nor is Hekate actually part of the original story, nor found in all versions of the story. In most instances she is in fact just a companion to Persephone in the story not the one who actually leads her from the underworld. That task actually falls to Hermes, Hekate follows behind Persephone and holds her torch(s) behind and above her to light the way.
In some of the pottery pieces and plays it is suggested that Hekate might actually be performing the role of guiding the child Persephone from the last remnants of her childhood into the passage into the first stages of her womanhood. To be performing her role as the birthing goddess who brings the child into the world, only in this instances she has brought the child from the passage of her trials and passes her as a woman into the world above t mark the end of her childhood. Making it a true Maiden (Hekate), Mother (Persephone) and Crone (Demeter) in the sense that Hekate is the virgin, Persephone is the mother figure who brings fertility and fecundity back to the land with her return and Demeter is the crone who gives up the sterility of winter's barren hold with her return to the surface.
The Lampadephoros persona ties into her Macedonian / Byzantine identity. Though historically it gets a bit confusing in that sometimes it's equated to Hekate, other times to Artemis. Though the crescent moon and star image have been used by many different nations and groups it still does not rule out a specific association to an historical / mythological event.
According to accounts which vary in some of the details, in 340 BCE the Byzantines and their allies the Athenians were under siege by the troops of Philip of Macedon. On a particularly dark and wet night Philip attempted a surprise attack but was thwarted by the appearance of a bright light in the sky. This light is occasionally described by subsequent interpreters as a meteor, sometimes as the moon, and some accounts also mention the barking of dogs. However, the original accounts mention only a light in the sky, without specifying the moon. To commemorate the event the Byzantines erected a statue of Hecate lampadephoros (light-bearer or bringer). This story survived in the works of Hesychius of Miletus, who in all probability lived in the time of Justinian I. His works survive only in fragments preserved in Photius and the tenth century lexicographer Suidas. The tale is also related by Stephanus of Byzantium, and Eustathius.
The Chaldean Hekate shows up about the same time as the Latin crone version of the witches Hekate. What is interesting is the Chaldean has the Dogs head, the Cows Head, The Horse head as a norm. Occasionally there is a 4th head that can be that of a dragon or that of a Lion. The Lion is said to be associated with Kybele / Cybele at times. The dragon / serpent though that one at times is said to be associated with the Hydra at times.
Harder to trace but sometimes equated to the stories that the Hydra guarded the swampy entrance to the underworld just as Cerberus guarded the island entrance. Hekate like Hermes also could come and go from Hades at will and drive the restless dead before her. Yet some stories claim she brought them in via a different route as they didn't need a coin for Charon the Boatman. She could also bring out the dead to place them as guardian's or dispatch them to punish if she desired. Again not needing to appease Charon or provide to the boatman.
It also tied into stories of her holding dominion over the waters. She held dominion over the land, sky and water. Yet as as secondary titan she didn't hold dominion over the deep water but coastal and inland waters. That gave her dominion over the creatures as well, that placed her in control over the hydra being a creature of the water and land. In that role she was also prayed to by fishermen and sailors and had shrines and sanctuaries in coastal areas. Ironically this is an area that is not spoken to much about in most pagan practices. Most tend to focus primarily upon her magical influence.
One thing I do find interesting is that the 29th of each month on the Latin calendar was listed as sacred to Hecate yet there are no sanctuaries / temples to Hecate in Italy. The Sanctuary at Nemi aka Diana Mirror is associated to Hekate because of the three figures associated on coinage with the sanctuary / temple. Yet none are specifically stated as being Hecate / Triformus. It is presumed / assumed due to the three figures engraved upon the coins mostly. There are some references to Hekate in Sicily with the temples to Demeter & Persephone but those predate the Roman's and belong to the earlier Hellene settlements. To my knowledge no sanctuaries / temples have been discovered for triformus either so the idea of the 29th being a sacred date or of importance raises questions.
From a Hellene aspect the primary calendar we have to go by is the Athenian calendar which was not utilized by all of Hellas (Greece). So the legitimacy of it's dates raises questions beyond the extent of how widely was it's influence and correctness for the other poleis (Greek city states). For instance we know Laconia (Sparta) had a different calendar than Athens did.
Different calendars and holidays would give rise to different holidays, rituals, ceremonies, practices, etc in how they worshiped. Historically it's know that even the 12 Olympian's were not the exact same 12 all over Hellas though the changes were relatively minor by only 1 or 2 changes. But it was often enough to change how a god / goddess was seen.
Consider Hekate in Athens was an outsider and foreign if we look at how Medea was seen and though of in the Argonautica story. She was not seen as an Olympian but as either an Titian or an outsider if you consider her placement in the Troy story. She is placed with Artemis in the stories backstory. Yet Artemis is aligned with the Trojan's and actually sides with them against the Olympian's in the sense she impede's the Hellene fleet. She is born on the Anatolian side of the sea and it is not until the war is over that we actually see the Olympian pantheon settle out and stabilize. But prior to the war and during the war you see the gods & goddesses align pretty much by where they "originate" from. Hekate's history ties her closely to Artemis and Leto and they are placed on the side of the Trojan's which suggest's Hekate originates there as well. Either Thrace or Anatolia / Caria.