I just wanted to give you a few ideas based on my own experiences and medical training.
1. Medicine can be wrong.
2. She could have a condition small enough to go undetected for years while stil producing symptoms for her.
3. Even If it turns out to only be somatoform in the end she really is feeling and experiencing the pain that she expresses. I know this from personal experience and extensive research. I possible way to diminish some of the tension and stress would be to acknowledge and validate her pain. Not dote or enable just validate. Possibly after awhile she might not be so defensive when you the subject up. Plus getting the depression treated should alleviate some of the pain. I hope maybe I gave you some food for thought. I'm not a doctor but I have been around the mental health block far too many times in my 28 years and it all fascinates me so I pay very close attention, I admit I'm no expert though. Best wishes. Please keep me posted. I will keep you and your family in my thoughts and prayers.
P.S. PLease make sure you remember to adress and take care of your mental health because if you get too stressed or depressed you won't be able to help anybody else. I hope all calms down for you.