She can check her bank statement by going to an ATM or accessing her bank's telephone banking service.
Tell her she's not getting anywhere near your laptop until she replaces the cream she stole from you, and that you don't trust her with anything of yours.
Your parents should not be letting her get away with crossing personal boundaries like that. The more they aid and abet that behaviour, the more she is going to expect you to share what is yours with her.
Just because she is a guest in your home, doesn't mean she has to be a guest on your computer.
If push comes to shove, and you have to let her use it, create a Guest account with very limited access. I'd also be inclined to NOT leave her unattended. I might even offer to look up the bank statement for her. Ask her for her account number and password and say you'll look it up for her. If she's not willing to share that info [of course she won't be], then say "Sorry, I'm not willing to let you cross my boundary either. Get lost, Freeloader."