Has she tried physical therapy? Being a male I can't really offer any personal knowlege of how breasts affect the back, but I have undergone quite a bit of physical therapy and surgury for disc problems. A physical thereapist can individually evaluate each patient and devise a set of exercises specific to the needs of those patients. I wish I had gotten my posture corrected and put on a program of back exercises when I was growing up rather than at 34 when I started having back problems.
There isn't anything that will help this. I had a reduction and it was the best thing I ever did. Imagine having to wear a bra all the time, even when relaxing at home. Imagine that you have to wear a bra under a nightgown if you want to look nice and not like a cow. I had my reduction over 10 years ago and it's only now that the lines on my shoulders are going away from the bra straps digging in my skin.
I'd go topless if I could, I'm so happy with the freedom of having normal boobs.