I almost feel like I am abusing her mentally the way some put their words here but I know it may not be intentional.
If you can't keep her out in a herd situation, or with another horse at least where you are, then IMO I would be looking for somewhere you can. You don't have to buy another horse if you can't afford it, there are probably other places around that allow their horses to be... horses. Or someone else with a lone horse you could share agistment with. Or even if no other option, a goat or sheep or some such.