This isn't like shooting a home intruder who presents an immediate threat to your safety or that of your family. That would be a justifiable homicide. Unless she can somehow couch this killing in "justifiable" terms, criminal charges are appropriate in this case. The prosecutor really doesn't have much choice, no matter how sad the circumstances.
At the same time, I certainly sympathize with the woman and her husband, and the ordeal they've been going through. Without knowing more of the facts, which I'm sure will be presented to the court, I'll speculate that it's very possible she could get out of this with a conviction but no jail time.