Like luvs said, no stalling, no grain. Lotsss of hay. My mare had ulcers and pepto bismol works well too if they start coming back. I'm starting my mare on UGard, which my BO uses on their show horses, so I know that one works well.
Also, if you notice she's developing them again, I wouldn't exercise her more than a walk because trotting, loping, and galloping splashes around the acid in their stomachs, which is painful if they have ulcers and you will have a VERY grumpy horse. Otherwise she should be fine. After my mare was treated, she lopes around just as any other horse.
Do you know what caused the ulcers? My mare is very anxious about everything and the vet figures that's how she got hers. She was pasture kept on free-choice hay, she's just kind of wound a bit tight. If your mare is somewhat like that, a calming supplement might help a bit to keep her worrying down.