why doesn't she want to? if it's because she's scared, i think everyone gave good advice (no pedals, scooters, etc). if it's something she just really doesn't want to do, has no interest in, i'd leave it alone.
why do *you* want her to? because you think she should, all the other kids do? i'd leave it alone. because the rest of your family really enjoys riding bikes together, but you can't because she won't? they make those bikes that hook onto the back of the parent's bike (
http://www.rei.com/product/752015) - maybe she'd see how fun it is for the rest of you and decide to try it on her own. or not, but at least you'd still be able to do it.