Spinal nerve damage

Sadie will be 7 in a couple weeks. She's been gimpy in the rear for a couple weeks now. She is sort of favoring her left rear leg...she doesn't lift it up all the way and sort of drags her toes on that foot. We took her to the vet and she tried all kinds of poking and manipulation to get Sadie to indicate where the pain was coming from to no avail (of course, we all know that GSD's are a very stoic breed and don't show pain easily). She was stressed at the vets office too so just kept pulling toward the door when we tried to get her to walk and show the limp that way.

But, in any case, she put Sadie on Rimadyl for 2 weeks and told us to see if it helped. She said we would try this first since we don't know where to focus xrays and they would have to do so many. If the Rimadyl does not help at all, she said it is likely neurological. She said a lot of GSD's suffer from degeneration of the nerves along their spine. I looked this up and it looks like it's called degenerative myelopathy.

Well, she's only got a few more days of the meds left and it hasn't helped her at all. Does anyone have experience with this degenerative myelopathy? I'm wondering if there's any supplements or anything I can try to see if it helps before we put her through xrays and more testing.