I trust everyone realizes the futility of assigning stats and rules to a TV show where abilities will develop at the speed of plot?
That said, I wouldn't make Sabrina half-elf or tiefling. This isn't a race or species thing. Witches are still human, just supernatural "heightened" humans.
(Especially the females. The males seem to have gained their positions of power despite middling ability mostly... because they're male?

)
I don't see any evidence of any racial traits like speed, grace or strength. (Or wisdom, for that matter. Just ask Mildred and the others who wanted to become Queen of the Feast



) Maybe attractiveness, but that's probably more "because Hollywood" than anything else...
In a show about Vampires or Werewolves, yes, traits based on race, absolutely. But here? This is more akin to a restricted
class choice. Regular humans can basically only be Commoners (which, in the context of D&D, covers basically everything from miners and waitresses to mayors and headmasters).
Sabrina & Co can choose the "Witch" class, which definitely includes spellcasting, but mostly of the indirect ingredient-heavy sort. Probably of at least two varieties that are most unbalanced - cf "full" and "partial" Heka Practitioners in Gary Gygax' Dangerous Journeys (read: some witches get ten times as many spell points as others, at least when The Plot wants them to). It also includes a few Monk-like physical upgrades (like long life).
This will help with "future compatibility", since it's fairly evident that Sabrina's friends will all end up with a "prestige class" of sorts - Harvey the Witch Hunter, Rosalind the Oracle and Susie the Ghostwalker.