She gets really stubborn about this and gets a little attitude. I try to be soft on the reins and use lots of cues but she would rather that I yank on her rein than use my legs for cues. In the saddle she does a lot better but bareback she tries to bite my legs and crowhop me off. How do I get her not to do that?
Will she do this to anyone who rides her bareback?
I admit I missed that you said that bareback was the only place this happended.
It could be that while riding bareback you are unwittingly gripping up a lot tighter with your lower leg. Mares can be really sensitive about their flanks, especially if they are in heat. Every thing you do in the saddle will be amplified to the horse when you are bareback, since there is no pad to deaden it.
Bareback is a wonderful way for riders to become more balanced and learn how to truly feel and move with the horse. But you need to remember, saddles muffle your cues - most people find horses are more responsive bareback. But if your horse is sensitive to being ridden in a saddle, bareback is even louder and more uncomfortable.
I'm going to put money down that she has pain somewhere - or that she doesn't know what the cue means. When I get on a new horse they always investigate my legs, when I apply pressure, they'll often look at my legs, nose at it, or fuss in some way or another trying to relieve pressure - it's not very often that moving forward is their first guess on how to relieve pressure.
So here are my thoughts - ground work! Do you do all sorts of yielding practices on the ground? Does she yield her hind end, front end, back up, will she side step?
If on the ground you put pressure on her side where your leg would fall - what does she do? Does she get upset then? If yes get a vet out - if no it's time to build her yielding and your dominance. If she yields perfectly on the ground, but is still upset being ridden I'd suggest her back or legs hurt in some way.
I think we really need more information. What sort of training has she got? How long has she been acting this way? Has anything in her diet changed? What skills can you do with her - ground and mounted? What is her diet now? When was her last teeth floating and vet check? Has she ever had a chiropractor or massage therapist?
I agree that it is probably a pain/discomfort issue due to a lack of saddle.
Saddles tend to create a barrier between horse & rider and the tree is designed to spread your weight out over a greater surface area.
Bareback riding can be good but only in small doses. Your seat bones are probably pressing on sensitive muscles (you also naturally grip more & apply more pressure when riding bareback, which may, for a sensitive horse, cause them to become upset)
It's more a test of a rider's skill than anything benificial to the horse