Suffering from Mitral Valve stenosis.

My sister is suffering with mitral valve stenosis due to heavy calcium deposits. And she needs to go for valve replacement but as she is not yet married and her family is incomplete. I want to understand which type of valve should we choose for her. Doctors said if she will have metallic one then she needs to take pills for rest of her life and that will create some difficulties to deliver a healthy baby but if she will have tissue valve then she will have a normal delivery but in next 10 years she will have to go for another surgery. Now I want to know which valve should be appropriate for her and also won't create trouble while having a healthy baby in future. And also want to know if we are choosing Tissue valve then how complicated the second surgery will be? Can it be a good Idea for now to go with a tissue valve and after 10/12 years switch to metallic valve when second surgery will be performed without any complications?