I really want to make this one for myself as it looks handy for walking the dog or running/walking for exercise. I appears that it would stay close to the body and, if worn cross body style, would be easy to reach the phone, etc. Wondered if this would work for your mom. I don't know if it would be in the way for her but maybe you can tell.
https://sew4home.com/slim-crossbody-...-and-hardware/