Sounds like the nurse is a bit out of date to me - the idea that stress causes ulcers went out quite a while ago. The vast majority of duodenal and gastric ulcers are caused by
H.pylori, as shown by Warren and Marshall in the 80s.
H.pylori is an interesting little bug. It produces an enzyme called urease, which essentially neutralises the microenvironment around the bacteria (any urea present is converted to ammonia).
H.pylori produces cytotoxins which damage the mucosa, opening the way for further damage by other bacterial products and hydrogen ions.
So, get rid of the infection to get rid of the ulcer. To do this, we use an acid suppressant and two antibiotics for one week. The americans use a two week course,but this is not really needed (increased risk of side effects, decreased compliance).
Some results from a quick google search:
Home | CDC Ulcer BBC NEWS | Health | Nobel for stomach ulcer discovery Helicobacter Pylori and Peptic Ulcer
Of course there are other causes of ulcers, the two most important being NSAIDs and corticosteroids. Both of these exert their effect by reducing the production of the cytoprotective cyclo-oxygenase-I enzyme. COX-II inhibitors should in theory be better than non-selective NSAIDs, but this is still being debated. I think the current evidence is that COX-IIs are better for minor GI effects, but there is not much of a difference in major GI side effects (i.e. bleeding ulcers). I've not had a chance to look in depth at the MEDAL (etoricoxib vs diclofenac) yet, so don't quote me on this.
So the role of stress is a minor side issue that doesn't have any effect on how patients are treated.