It totally depends on the hotel you are using. Hilton, for example has lower rates they call net direct that are only good prepaid. Travelocity and expedia are prepaid rates, etc. She can also call the hotel and just put it on her card, or get them a gift card to use, something like that if they say they won't take a prepaid (though I find that hard to believe they would turn it down).

American will even let you purchase gift certificates for a flight for some set fee for the US, a higher one for other places, etc, so they can pick the date and times they want to go, sometimes they are a good deal, sometimes not.