Just got off the phone with Dad.
Mom's been moved to the neurological ward, where she's going to stay at least another night.
Turns out surgery IS necessary, but it's not emergency, so there's the possibility it can be scheduled for sometime in January so she can come home, relax, and then make proper preparations for a hospital stay. Not sure what kind of restrictions she'll have on activity.
The surgery is disk replacement rather than spinal fusion, which is great news, because I haven't heard anything good being said about fusion. It's expected to be fairly outpatient if things go well -- surgery in the morning and back home by evening or the next day -- but I don't expect things to go well, because life.