Doubt she'll be liable for anything. At least with my credit card, I have 100% fraud protection. Debit cards are a different story and you can be liable for (I think) $500.
Buzz is dead on with setting notifications. Any charge over a certain amount and I get an email straight to my phone, also goes for cashed checks and transfers on my main bank account - now that "Payment by Check" methods are starting to be exploited big time.
The other suggestion I'd have is using One-Time Credit Card Numbers, if your bank provides that service. For instance, if I'm making a purchase online from a company i'm not 100% confident in, I can go to my BofA account where they will issue me a unique credit card number tied to my account and it can only be used for that one purchase. Has saved me in the past... also good when signing up for "Free Offers" that you need to cancel within 30 days.
More info over here:
Shop Safe | Credit Card Fraud Protection with Bank of America