My mom had an aortic valve replacement surgery and now she's afraid that if she gets stressed it will "blow". could that happen?

Modes AVR failure: There are two kinds of valves, mechanical and tissue. Mechanical valves don't tend to wear out. Tissue valves will fail with time, but usually don't "blow out". With time, tissue valves will become hardened, rockier, more difficult to move, and this tendency increases with more strain from higher blood pressure, but as a trend over time, not as a blow out. It can give way at the end.