I have a mare that I have not ridden outside of the pen because every time I take her out she acts up. The other day she reared up on me and then bucked and trough me off. She makes me nervous because I don’t know what she will do next. How can I stop her bad behavior when I’m on her?
You need to do quite a bit of ground work with your mare before you ride her again. She is simply not ready, even if you have ridden her a bit.
I really need much more information from you before I give you more definite answers. How old is she? How long have you owned her? What experiences has she had before you? Is she in any physical pain? Horses have reasons for everything that they do. She at least needs to learn to be lunged correctly. If you are not familiar with correct lunging techniques you need to learn them. It is really a skill and an art. It is designed not to tire the horse. but to teach the horse a basic discipline in all three gaits, to learn what your body language and voice mean, and to lower the animal's energy...NOT by chasing it around and making it tired, but by establishing "submission" in a good sense.
Then once lunging is easy and almost boring to her, you will have an experienced ground person lunge you on the mare. Then she has two people telling her the same thing. You need to go back several steps. In the end, it will save you time and trouble and you need to be safe and fair to the horse.
I could give you more definite help....email@example.com, www.MitziSummers.com