This happens to me quite often. I've talked with my doc about it. I try to avoid foods with salt, etc. At least part of my problem is that I am short. Airline seats often leave me with my feet not touching the floor; so I have learned to put a bag under my feet and also an airline pillow under my legs to avoid the pressure of the edge of the seat. Also I find that most chairs used for meetings are horrible. For me that adds to the problem.

I hope this helps your mom. I know how nasty this problem can be.