New horse? Then ulcers are definitely a possibility. I would assume she has them and treat now.
Otherwise, we need more details. How long have you been offering her peanut hay and in what situations? If she is out all the time on good stockpile winter grass pasture, she may not have any reason to try an unfamiliar to her type of hay. If hay is only randomly shoved in her face when you bring her up to work with and she’s by definition in a stressful situation, she may not be hungry or comfortable enough to eat it. If she’s stalled for long periods or out in a dry lot/mud pit with nothing else to eat or do all day, then it is odd if she doesn’t develop a palate for it pretty quickly. If it’s offered in a herd situation, then she may be too intimated to approach or compete for something she doesn’t yet even want or like. Again, it depends on situation.
If she’s never received for liked any type of treats, then wouldn’t be concerned about her rejecting stuff like fruits/vegetables/mints/crackers or other junk now. If you want use treats for training and it is important to you, then I recommend trying what a lot of mustang folks have had success with for this purpose. Fresh off the range mustangs have never seen any kind of grain or pellet or treat. And they are also super stressed out. Many/most don’t accept those foods initially. Once they are eating hay and less stressed out in their new environment, then start leaving different pans of different grains and other types of feeds and treats for them to maybe try out in their stall/pen when you’re not around and stressing them out. When free of all outside stressors, then most will end up getting curious and comfortable enough to taste test some things. And most will find something they like eventually, if left to their own devices. Then you can use that as feed/treats. In some cases it will take a long time, though, so don’t just dump some random stuff in her stall for a few days and then stop if she doesn’t eat it. Repeat it for weeks or months.
