You say "keep your fucking hands off my toothbrush or else, bitch."
Seriously, that's a really personal thing, right up there with your underwear and contraceptives. Anyone i've known for only 2 weeks, whether i'm fucking them or not, does not even THINK about TOUCHING my toothbrush, forget about moving it from its rightful place in the bathroom. Who the FUCK does she think she IS? That's like rearranging my furniture or taking away my coffee and replacing it with decaf. Who DOES that in someone else's house? I've been MARRIED for over 10 YEARS and even my own SPOUSE doesn't do shit like that.
She wants your man. She's trying to take your place.