A) It's Mandy's character. She NEEDS to feel powerful. She didn't want him to have this power over her, so she got the make over to get it back... meaning she is probably into some kinky femdom stuff, if she ever does fucka guy
B) This episode was made to show "a way to get your control back". Don't think it was targeted just for little girls either. Imagine the power-gasm you would have had if Stacey suddenly got wet and wanted to jump your bone, then you could tell her to fuck off. Note: power-gasm, not orgasm.