is it normal for au pairs to use your toothpaste, shower gel, shampoo, conditioner, etc?
well, yes, if you haven't bought her any. You would buy all that for a family member, wouldn't you?
I would buy her own supplies (including sanitary pads and tampax, just one pack of each and ask her what she prefers).
Au pairs are not paid enough to have to pay for basic things, sorry.
My bathroom has a lot of products on shelves for anyone to use, family, guests, kids friends - shower gels, shampoos, conditioner, toothpaste, got packs of tootbrushes if someone needs them, cotton, and so on.
My own stuff is safely stored away.
Don't buy her make up, but I think it's up to family to buy basic supplies.