My mother fell, shattered her femur bone and had to undergo emergency surgery for repair. She had general anesthesia and my mother was talking fine the day before and now she can barely communicate. She had a MRI performed to look for signs of a stroke. The test came back negative and DRS do not know why this is happening and cannot provide a reason for this. I know falling can be traumatic for the elderly and hopefully she can regain her speech again.
In the young nurse's case, her stuttering went away after a few weeks of therapy. I have no idea if that's what's going on with your mom, but it's worth checking into. You can also google sudden onset stuttering and look up the possible causes. Stroke is one, but it sounds like they've ruled that out in your mom. How old is your mom?
How long is it since she had the surgery? can she still do other things as before? she is still probably receiving strong pain killers which she does need in the early days and these effect people differently and she may be better when these can be tapered off as the pain lessens. Is she able to eat and drink? All you can do is hope her speech returns within a few weeks. She can have help from a speech therapist. Keep in touch. Other people will have had experience with elderly loved ones needing emergency surgery.