the horse is probably the girl's best friend, and he's probably enjoying the attention. i had a horse when i was that age and spent most of my time with him, brushing and braiding his mane and tail, teaching him tricks and basically treating him like a pet dog. he loved it. i think that given their choice, most pets would rather be dressed up and fussed over than completely ignored as so many are.

(by the way, this appears to be a gelding, not a stallion. much better choice for a child.)