Do you not want to give her her own user, and just put a password on your own user? Stop her getting at any of your stuff?
If there is stuff of yours you do want her to have access to, you could put all that in one (or more) folders in your user, and then "share" that with her user, to give her access. Any other stuff of yours, wouldn't be visible.
There might be a way to password protect some folders, but I dunno what it is sorry - and it would bug the shit outta me, having to input a password for stuff on my own pc everytime I wanted access.