Later we learn that Amy is a “Fire Witch” (i.e. aligned with the element of fire), who although having taken the time to point out magical consequences to Xander (with his love spell), fails to fully consider them when she turns herself into a rat (to escape being burned at the stake). Unfortunately, Amy is unable to turn herself back, and for quite some time, Willow does not know how to turn Amy back either.
Eventually, Willow succeeds and Amy resumes her human form (albeit with some “ratty” behaviour). Being initially somewhat scared, Amy casts two quick spells (with green smoke swirling from her fingers): one to close the windows and the other to pull the curtains. Eventually, Amy wants to “get out” into the world again, and together with Willow, they both enjoy an evening of spell casting: Willow plays pool with magic, Amy magically calls a woman over (for Willow), Willow changes the band, Amy makes a man fly (like an angel), Willow changes the height of two men and Amy changes some dancers into sheep. After having abused their powers, they both become tired (from casting too many spells).