Alfalfa is a good natural stomach buffer for horses and small amounts added to her other hay may be all you need. Smartpak offers other supplements that can be helpful for digestive support and it looks like you’ve discovered them. You can also offer small amounts of alfalfa before you ride so the buffer is there and the grass mat in her stomach will prevent acid splashing and irritation while you ride. If you notice signs consistent with gastric ulcers you should talk to your vet and have her scoped to be sure. Proper ulcer treatment is necessary if she has any. Good luck!