Why? She did everything perfectly, obediently taking the drugs and doing the care and fucking exercising and staying in shape, and made the first one last more than twice as long as anyone expected it to. By schedule she would have needed her third replacement, not her second (so her fourth heart total, not her third). If anyone deserves it, she does. She'll probably make this one last until she dies of some other old-age related thing.
It's not like she's elderly and won't get to use it for as long as it can last. At 50, with her son in college, she is probably very needed for another 20 years, and if her son makes any babies then they will want to meet their grandmother.
I just hope that when my (or my wife's) ticker goes, we won't get denied for being fat and lazy (and less needed because child-free). This lady deserves it more than I will.