12 year old female schnauzer?

I have a 12 year old female schnauzer that is having problems with her hips and rear legs. She will just be walking around, rear legs will start to tremble and she will either just sit down because her legs basically fall out from under her or she will fall over and has difficulty getting upright. It doesn't appear to be a seizure and she doesn't seem to be in any pain. She had a complete blood work up and no problems there. I'm taking her for radiographs on Monday of her hips and she is under the care of a great chiropractor. If anyone has any suggestions or experience with anything similar, please reply. She is a very sturdy little dog and has never had ANY health problems. This started approx three weeks ago and seems to come and go. Thanking you in advance! Marty, Heidi and Fritz