Ditto, if she’s…ahem…inviting the geldings to hook up for a day or two then telling them to get lost for the next couple of weeks, it’s hormones. Tried the supplements on mine, the only ones that did anything were the ones with sedating herbs, mostly Valerian, then she was just out of it. We showed so couldn’t use them. Regumate 6 months of the year worked great. Long as the other horses kept their distance, she didn’t start anything yet still never a fan of being crowded.
If shes just a byatch around other horses, she’s just a byatch around others by nature. Some mares are like that, had a couple of geldings that just didn’t like others in their space too. Have to manage that by watching your turnout buddies and being sure they get along and/or having plenty of room.
Be aware supplements won’t change basic behavior unless there is a true deficiency. Even then, you can address the deficiency and still have a byatch. You can’t fix everything with a vitamin or herbal supplement. Despite marketing and internet miracle cures for bad behavior. Not sure you can really fix anything behavior related with supplements.