I would put her on a supplement to keep the ulcers from coming back because horses that get them can keep getting them and are more susceptible to them. I am worried about her food choice. Alfalfa pellets are very high in protein and it seem like she does not need it because she gets nervous and seems like a hot horse. Personally it sounds like your horse is stressed out and nervous, these things can cause ulcers. Additionally I would try mare magic with her to calm her down so she could possibly go out in pasture. Also you can try magnesium, that helps them calm down and focus more.
I would talk more to your vet and also the owner of the horse. Be there for vet appointments and if you can't make it call your vet and talk to them about what you need to do.
Now, diatamichious earth. How many cups are in a scoop of this? Horses should only get 1 cup a day of this. Why are you feeding this? Does your horse also have a problem with worms? What DE does it act like a chemical and it actually dehydrates the insects. This has more information on it: Diatomaceous Earth - Food Grade Diatomaceous Earth Health Benefits
When you say they are going to switch her to wellsolve is it the weight control one or the l/s (low starch low sugar). Why does she need to switch to this? If she is under weight don't go on weight control, and it doesnt seem like she is special needs and needs the l/s one. Here is some info about it: Purina Horse Feeds - WELLSOLVE
I am little confused on what she is eating. Can you please give more info like height, weight, work load, how many flakes of hay, type of hay, amount of beet pulp, rice bran, grain, and DE. This way I could help you even more:)
The best advice I can give you is call your vet and see if you could get his/her input on what you should do for the ulcers and what you should do for feeding because I think it should be revised.
Also if your horse grinds your teeth, she probably needs floating even more! What happens is the teeth keep growing and the more the horse wears them down by grinding, chewing, etc. they start to develop hooks on the sides of their teeth. Please read the first article on floating, that explains it better than me:) Dental Care: Floating, Hooks, Loose Teeth, and Wolf Teeth
I hope this helps! :)