its a dominance thing! i think people said that if the little one was spayed, it may help. but it doesn't always mean that it will! her humping is showing dominance!
Avie has a favorite toy.. it's her monkey!
i've heard of alot of furbabies having a favorite toy.. and sometimes they will do this, especially if the toy is on the bigger side(closer to the size of your yorkie)
i would just tell her no or let her know not to do that!
