I do not want to belittle this scary sounding diagnosis but most of us at a beyond-youthful age would probably get that attachment. Check this link http://www.webmd.com/back-pain/tc/degenerative-disc-disease-topic-overvi… to get a little more information.
Since the doctor has cleared her for exercise, I would just use the precautions for anybody with potential lower back problems. Make sure she communicates well with you about anything that causes her discomfort. Since she is in a small group setting, people are sometimes self-conscious about asking for modifications.
Hope this helps.