Personally I'm a little weirded out that she was carrying two hearts around in the first place:

British doctors have revived a 12-year-old girl's dormant heart and removed a donor heart which she had started to reject, hospital officials said late today.

According to the article, artificial "assistant" hearts are used in cases like this today. I think perhaps I'm just not understanding what the heck is going on here. Regardless, it's still a good thing for the girl.