Spend some time with her, without riding. Just lead her around on the trail, let her graze, work on ground manners, take treats for when she's being good, etc. Do NOT ride her until you get a saddle that fits her.
I would also would have an equine chiropractor out to visit her. She may be hurting besides just the ill fitting saddle.
DO NOT punish her AFTER bad behavior. That doesn't do any good as she doesn't know why you're punishing her. You can swat or reprimand her DURING a bad behavior, but not after. If she acts up like that again, you need to put her in a small area and keep working her until she behaves. Then praise her and quit.
Also, if she's on any grain, take her OFF. Any grain or feed products make my moody-mare much worse... She's on hay, hay pellets, flax, and a vitamin supplement now and she's doing much better
Keep in mind that most mares are "thinking" horses. Like the old saying, "You can tell a gelding what to do, ask a stallion to do something, but you have to Discuss it with a mare." You can't just hop on most mares after not working with them for a month and expect them to be perfect, especially one you haven't had for years and aren't well bonded with.