Do a little research and get a gift card she'll actually use, something for herself, not the daycare. Teachers and day care providers have loads of "World's Best Teacher" mugs and stuff that collects dust, but I know from what they've told me over the years that well-chosen gift cards are what they really covet.
Find out where she'll actually spend the money -- if she likes books, then a book store within a reasonable driving distance, not one at a mall miles and miles away; or if she loves to cook, a gift card for a kitchenwares store or housewares store. Be clear why you chose this card --Say in your holiday card something like "I know you love to cook so please use this to get a new kitchen gadget that will make your cooking even more fun!" etc.
Or ask her what local restaurants she recommends, as if you were going out yourself, and she'll end up telling you about her favorite places to dine! It takes some research but is worth it.
Please resist coupons or certificates for truly personal services like manicures, pedicures, haircuts, massages etc. unless you get them from the salon or nail place she already uses. Not everyone gets manicures or wants a new stylist to work on their hair when they're used to someone else doing it.... You could ask her husband, if she's married, or someone else at the school what she'd welcome or where she shops. Good luck and have fun!