I agree with getting either something "disposable" that she'll need lots of (diapers, especially sized up, or shampoo, etc) or something that a new mother might not know about or buy for herself, such as:
Robeez or See Kai Run shoes for baby, sized up to enjoy when he/she is walking
a special blanket (my son got a beautiful Cherish and Joy blanket that I'd never have bought since it was very expensive, but he LOVES it, and it's the softest thing I've ever felt)
a gift card to a parenting website like Mom4life or babyuniverse, so she can buy things later as she needs them
a baby sling (many mothers think they won't want one until they try it)
Or, if nothing else, how about a few subscriptions to parenting magazines? Then later, a subscription to BabyBug for the baby.
BTW, I love the library idea!