The shield will break if she stops concentrating on it/does something else. If enough damage is done, the energy it takes to keep it up will be too great and she will have to abandon it.
Yeah, she killed them. However, it hasn't been traced back to her. If that's a problem then I can change it.
EDIT The shields also don't protect against temperature or any kind of attack to the mind, only physical matter. She's vulnerable to attacks on the mind, which I can't believe I forgot to mention.