It's a long shot, but are you sure your Mom hasn't sustained any sort of injury? Sometimes what seems like a simple slip and fall is enough to cause a whiplash that can bruise the spine. For a person with a small canal and natural degeneration, even "sleeping funny" could cause a problem.The contusion can clear before an MRI is done but the damage to the nerves can persist.

In addition to the symptoms you listed, you might want to ask her if she's experiencing a burning sensation at the back of her head. Also check to see if one of her hands is swollen.

I can imagine how stressful the not knowing is. She's lucky to have a daughter like you watching out for her.

Good Luck