I’d also suggest something riding related if she can use it - justforponies.com lets you shop by color if you know what her favorite color is. One of the good things we’ve gotten recently is a fun colored gloves but helmet covers, belts, and socks work too. Saddle pads are good if the barn lets her use it.
Something that she can keep at home and probably enjoy a lot is a Breyer Gift set, like this one. It contains the horse, a rider, and tack. My girls love them.