I highly suggest that your vet retake the xrays to include the neck. If she has IVDD it can affect her back and neck and this time her neck appears to be affected. I highly recommend at least getting her started on an anti inflammatory and cage rest. The fact that this is bothering her down her front legs tells me that the condition is more advanced then she is letting you believe. It may not be a bad idea to visit the neurologist or have an MRI performed if you are up for that expense. If she develops stiffness in the front legs, inability to move both front and back legs, or increased pain then a trip to the vet needs to be made immediately. Time is of essence with this condition because the longer one waits the less likely chance she will have a complete recovery.
Please let me know if further assistance is needed.
Theresa
A Voice for Your Pet
15 years experience in small animal medicine