Yep. She can call ahead of time and use them to buy OBC - I think it's in $25 increments, maybe $50?
Or she can put them on her account at Guest Services once she's boarded.
I would suggest she merge them onto one card over at disneygiftcard.com because anything left over will go back to the form of payment, so it would be easier to only have ONE card to deal with it coming back to than have a lot and try to figure out which it went to. (Like the guy at the subway turnstile today who seemed to have help onto every card he ever had whether it was empty or not - I know he missed one train trying to find the one with something on it. LOL.)