I agree w/ FH. If you want to give a gift, be sure to include a nice note w/ it. That will mean more than the gift.
The gift can be just a token, but ti should be something sort of "personalized" - something that when you saw it made you think of her. A nicknack that looks like her fav horse, a t-shirt/plaque/bumpersticker/magnet w/ a saying that reminds you of her or one of her horses, maybe something you made (if you are crafty), a framed photo of her horse(s) (you can take the photo and then buy a frame).