My horse, Dreamer is a 12 year old Quarter Horse/ Appaloosa cross. Sometimes she is the best horse ever and does everything I ask her to and sometimes she won't do anything. I mostly just trail ride her around my house and sometimes work in the arena. I have a really good relationship with her on the ground. I do natural horsemanship with her and she responds really well. When I get in the saddle, though, she just puts her ears back and won't do anything I want her to do with out a lot of persuasion. She isn't sore or lame and I don't know if maybe she's just bored or something? Again, she only is like this sometimes, and the other days she is an angel so I don't really know what's causing this. Does anyone have any ideas on helping me with this? Thanks.

There's your answer! Could it be she is like this when she is in heat?

It is when she's in heat but it's more often than that too.

Check her withers, is the saddle rubbing making her sore?
Check her teeth, do they need to be floated?
What about her feet, are they properly trimmed and comfy?
Finally, check your attitude, are you the lead mare or is she?

thanks for the suggestions! We can pretty much rule out the first three. I have an awesome relationship with her on the ground. She follows me around and everything but them when we get in the saddle she just wants to do her own thing.

She doesn't mean that you don't have a good relationship w/her at all! I have a wonderful relationship w/Jackson, but he is pretty disrespectful. He follows me around also, but there are times that if he could talk he would be saying "forget you, I do what I want!".
Try getting her in a small area. Carry a whip/crop(Not to hit with!) Walk around, and everytime she comes close, chase her away. In the herd, a dominant mare would do this to assert dominance, not letting her return to the herd until she shows proper respect by putting her head down, licking and chewing, etc... I don't mean to sound condescending, I just don't know what your entire back ground is. Horses don't go by people logic, we have to learn what they understand and respect and use that.

If your saddle truely fits properly, and she has had her teeth floated with in the last 2 years, and she has nice big shoes on. Then here are a few more suggestions.

She is at the right age to have her hock joints start to fuse. This can be a very painful process.

Also as far as her heat cycles go. A mares cycle is about 28 days but they can come into heat and ovulate every 14 days. You may want to track her cycle a little more closely. It could be that one of her ovaries is more painful then the other when she ovulates but they are both uncomfortable.

The biggest thing is that you need to figure out wether it is behavioral or physical, once you determine what it is, you can go from there.

You may need to have your vet do a good "lameness" exam with flextions and maybe even ultrasound her ovaries if nothing is positive on the lameness exam, (this way you know exactly where she is in her cycle to keep track). That way you can rule out if it is physical. Once you talk with your vet you could also ask him about using a bute to see if it helps.

Had a mare once that had painful heat cycles, at first we were not sure what was going on, her lameness exam checked out fine but we were still not sure what it could be. So we decided to try using bute to help diagnose. We would bute (a low dose) her the night before and the morning of a ride to see if it made a difference. We found that it did seem to help, so we went back to the drawing board by this time it was late spring and about twice a month she would act cranky when she was ridden, then we noticed that she started to colic mildly about once a month, but would be fine with a little banamine. We decided to ultrasound her after a colic episode and found out that she had just ovulated. In her case her right ovary causes her considerable pain at ovulation causing the colicky episodes but in general she would have uncomfortable ovulations on both sides.

Hope this helps but like I said check her physically first if it is not that then it is her behavior, and that will take some training. Good luck.