A related discussion, CIDP-Can you help? was started.
The progressive muscle weakness at the initial illness could have been due to a muscle disease, critical illness myopathy, or critical illness peripheral neuropathy. These disorders occur in ICU patients who typically have been given large doses of steroids over several days to weeks. GBS should also be considered, but given the normal spinal taps, this is less likely. However if she recovered from this event and now has new symptoms, then the two events may not be related. I hope this helps, good luck.
Any autoimmune or demyelinating disorder can mimic GBS. One of the clinical features of GBS is elevated protein levels in the CSF fluid evinced on the spinal tap.
By the way, don't be too quick to accept the doctors' belief that this may be an "emotional problem." If a 52 year old woman cannot walk without assistance, it's NOT an emotional problem, it's a physical one. If the doctors who are caring for her cannot reach a diagnosis or conclusion other than one emotional in nature, find yourself another doctor, preferably at an academic health center. Also, note that when something is labeled as a "syndrome" like GBS, or chronic fatigue syndrome, or post-concussive syndrome, it's a fancy way of saying "we don't know how exactly to explain the symptoms, but we're not ready to discount them either." A "syndrome" is an amalgamation of symptoms that are consistently seen in patients but which cannot be clearly explained by conventional clinical diagnoses. Doesn't mean something isn't awry. Something very well could happening. Doctors routinely attribute a wide variety of physical symptoms to emotional causes, and it's easier for them to label conversion syndrome (or somatoform, or hypochondriasis, or even malingering) than it is for them to say "I don't know." While emotional problems (such as stress, depression, and anxiety) can cause a wide variety of symptoms physical in nature, I doubt highly that they can cause the inability to walk in a 52 year old woman.
Get to the bottom of this. You're off to a good start. And also, you mentioned that a test was not performed because of insurance reasons. Never let that happen either. It's better to pay out of pocket and have a necessary (or potentially relevant) test done than it is to let the HMO dicate what's what. If the test shows something ultimately, you can EASILY recoup the out of pocket costs, otherwise the carrier faces liability (lots of it, too). If the test shows nothing, then you can't recoup the couple hundred dollars, but at least you'll have peace of mind. Which, as they say, is priceless.