Why not just sell her and find a nice gelding instead? I think it would be cheaper...

But now that you mentioned heavy mood swings, there are veterinary treatments for that. There's a mare int he College barn right now that had a hormonal balancing implant. It actually worked quite well, she doesn't throw herself at the door anymore when people walk by and we don't risk having her kick the sh*t out of while trying to clean her udder.

Look into the cheaper and less risky stuff before looking into spaying her.. :S