What do you suggest if my mom had an aortic valve replacement surgery and now she's afraid that if she gets stressed it will "blow"?

Relax, Revitalize: With current aortic valve surgery after adequate healing your Mom should really have very few limitations as to activity, and the surgery should actually allow her to do more. I have many patients that have gone back to running marathons, lifting weights, skiing,etc.. She should go on a gradual rehab program starting several weeks after surgery but within 2-3 months ,better than preop!