If she just started this, there is a good chance it may be because she is in heat. The only time any of my girls have ever humped anyone was either right before their heat cycle or during their heat cycle. They can become such horn dogs, lol. As soon as they are out of heat or shortly thereafter, they stop.
It could just be a dominance thing but if it just started during her heat cycle I would be more inclined to think that was the cause.
Either way I would discourage the behavior. |