SUMMARY: Being off drugs helps; being in hospital helps.
Sisters report that, two days after being taken off the drugs I was most suspicious of, her voice has come back and she seems to be mentally completely Mom again. Plus now she's in the hospital getting IV fluids and meds to deal with some other snowballing nasty side effects. I'm hoping she'll be home again within a day or so and completely back to normal. More tests are pending.
Drugs she was taken off of were Vicodin and oxybutynin (thanks, dad).