As a past provider I will let you know that a weeks pay bonus was never expected and would feel very uncomfortable. Also you need to consider your own budget, which we know BTW! I was always happy with a gift card to a book store, dinner, my favorite was a bottle of wine with a message from the kids. I still hang homemade Christmas ornaments that my past kids gave me on the tree.
Also, you could get together with the other parents and if you know of a big ticket item that she would like for her program buy that! I would have loved if for Christmas I got a new set of wooden block and shelves to put them on, or a new play kitchen with table chairs place settings and healthy food! How about a food share if there is a local place for organic fruit?
Good Luck!
Gift cards to the spa or for a hair cut always left me wondering 'how bad do I look at the end of the night, unless you know she frequents them, don't do it..