Like others have said, your stateroom keys can be linked to your personal credit cards, so as long as you're charging something to your room and using your own stateroom key to do so (and not your sister's), it will be charged to your credit card. In practice, it's really no different than using your own debit/credit card anywhere else, since any cocktail lounge, coffee bar, or shop will ask for the stateroom key (or MagicBand) at the time of payment.
My partner and I used this to make our trip budgeting a bit easier, and it worked flawlessly — we linked our cards to our stateroom during the online check-in process, but I'm sure Guest Services can set it up for you as well.