I am sure that whatever you choose to do would be appreciated -- everything from a handmade card by your daughter to an expensive gift.
My SIL used to work in daycare and she always appreciated gift cards because she could use them and get what she wanted -- even $5 cards were appreciated to places like fast food restaurants, Starbucks, etc. She also appreciated when the kids had "helped" with the gift, rather than it just being from the parents.
For christmas, we made the assistant teachers/after-school crew leaders, etc. a "movie night" basket. I found small baskets, popped popcorn (no butter) as basket filler, then filled each basket with a box of movie theater candy (dollar store), a packet of microwavable popcorn, and a $5 gift card to Blockbuster. The kids helped me fill the baskets, and wrap them with cellophane. Then they made little fit tags that we attached for each teacher. They seemed to be well received.
I also think gift cards to bookstores are well received because the teacher can either get something for herself or something for her classroom. We got the main teachers gift cards to the bookstore, and created homemade cards with the kids pictures on the front. DS wrote his own note on the inside. DD dictated hers to me and I wrote it, but she signed her name.