What questions should we ask when my mom goes to talk the surgeon about getting a heart valve replacement?

Many questions. Ask about personal experience, outcomes (survival, stroke rate, renal failure, sternal infection rate), length of stay post-op, type of valve used (biological vs. Mechanical), possibility of valve repair rather than replacement (depending on the valve involved). Get benchmark numbers from the society of thoracic surgeons (sts) website or http://www.Hospitalcompare.Hhs.Gov.
Several. Make sure you are at a place where they do a lot of valve surgery. You should ask what kind of valve they will use and why. In some cases, that determines whether you will need to stay on anticoagulant medication. Can the valve be repaired rather than replaced? Especially if it is the mitral valve, sometimes a repair is preferred but not every hospital is prepared to do that surgery.