I fractured one of my lumbar vertebrae (can't remember the exact #) in high school and didn't see a doctor about it till about 2-3 years later. Until I started physical therapy I found deadlifts and squats pretty dreadful and I couldn't lay down or sit without pain. I had to stay pretty hunched over sometimes and I couldn't run since I couldn't support the impact.
Did your fiancee go through physical therapy? That was the only thing that helped me. I had to go through about 6 months worth and it worked wonders. As well, I had to get some pretty painful massages on the right side of my back since it got extremely knotted and inflamed, I suppose from trying too hard to support my spine.
After all that, conventional deadlifts are still a little iffy for me. Push-ups and planks are still extremely difficult and I definitely pay for it if I ever let form slip. However I can do sumo deadlifts perfectly fine with zero pain. They are my favorite lift in fact!
If physical therapy isn't something she's gone through or can't see one for whatever reason I can give you all the exercises I did for it.