I wrote a couple of things in med school, some of which are still in use.

There are a lot of big players in the medical marketplace.

I would think a very specific niche app of some kind would be most successfull - as in "Helping a diabetic patient report and review their glucose levels with their physician" versus "an all purpose portal where patients can review all their information with their doctors." - you an probably get great ideas from your GF as she goes through.

BTW, I would offer this unsolicited advice: have some patience with her for the next 10 years or so. Medical school can be a major stressor. She may not have time to tell you how important you are to her...