For Sara, school is a mixed basket. She's clever, and has a fast, ingenious, goblin mind. Focusing on schoolwork is a struggle for her though, as there's almost something more interesting than schoolwork to catch her attention.
Transfiguration - Transfiguration comes more easily to Sara than any other kind of spell-casting. This is heightened by her second wand core— Demiguise hair.
Potions - Sara doesn't like potions very much (she sees them as rigid and boring, just following a bunch of steps), but she's pretty good at them; they're relatively straight-forward for her.