The problem was that she was intimidated, threatened and frightented to death of being killed is she testified - but the conundrum was that, if she DIDN'T testify, the monster would be set free and she WOULD end up dead.
Do you have familiarity about this case, beyond what the article in the OP says? Or are you inserting your personal opinion as fact?
The only way you're going to get the straight facts is to check the pleadings, which we don't have. But it is certainly possible that the prosecutor was trying to protect the victim.
If I had a dollar for every domestic violence victim who refused to press charges and wound up dead . . . they refuse to testify for a lot of different reasons - frequently they are not rational about their situation, or they are afraid of the partner. Sometimes, victims try to extricate themselves from the situation on their own and wind up 'setting the guy off'.
Just because other charges have been made means little. The guy could make bail, then go home and kill the victim because he blamed her for his problems. I've seen it happen.