She actually comes off as a high level Seneschal Witch (her younger self is more like a Distant Grasp Psychic, but even an Imperial Sorcerer would make sense, due to her non-Oz heritage).
Her familiar is the repository for her spells, which would be the Grimmerie (the spells she prepares are the ones it shows to her). It’ll be an Object Familiar (flavored as a book) that she can carry around and stash in her bag.
Mandatory is her Cackle, Cauldron, and Witch’s Broom at lvl. 14 for her flying.
Outside of that, she has ♬unlimited♬ capabilities because she can access the Grimmerie (which the Arcane spell list fits really well).
Alternatively, you could do a Spell Substitution Wizard with her Arcane Bond being her Spell Book (Grimmerie) and the ability to find whatever spell she needs is searching through her book (Spell Substitution).
Combat was never the main focus of the story, as Wicked is also a postmodern commentary of issues in the early 2000s (animal rights, government distrust, and racial conflicts) which the musical focuses a bit less on for the sake of entertainment (and hard to do fantastical special effects on the stage). So, she’s focused on trying to socialize with people and not harm them, but to only have her actions be misconstrued. So it’s more scant on what her actual combat abilities are.
As a Distant Grasp Psychic, she should be focusing on Telekinetic Projectile and then Unleashing Psyche (losing control of her emotions) for powerful telekinesis. At lvl. 16, she gains Constant Levitation which is definitive of her iconic power, which is flight.
But as the Wicked Witch of the West inspired a lot of other modern Witch tropes, so the skies the limit (no pun intended here).
Edit: I forgot. Part of the story of her evil magic powers are propaganda. She’s overall pretty tame. But since she did make good friends with a lot of animals, Summon Animal would fit as her main gig. Wilding Steward fits with her theme, her hex (try to be diplomatic and not be harmed), while also granting her Summon Animal.
