That's a tough one! Probably the best situation would have been if you could have gotten to know them first, but that's in the past so all there is to work with is the here and now!
Hmm...treats? You've probably tried those. But you might try calling her mommy and asking if there's any really SPECIAL treats she has that she doesnt get much, as those might be more convincing!
That's all I can really think of. Maybe try using a favorite toy too or something. Best of luck! Let us know how it goes, if you can!