Hi - it could be a disc herniation irritating the nerves that innervate the disc or PLL. These structures are linked in innervation to the sympathetic trunk and so could have caused her ill feeling.

In the end, if you can't diagnose what it is, you can't treat it. If there was no back pain then perhaps it is Wikipedia reference-linkSIJ (think Fortin's area of pain). At that age, she is a candidate for spinal stenosis - either canal or foraminal.

Let us know what goes on.. Thanks