Yep, I agree with that. But, once she had it, they've gotta deal with that particular situation. As a few of the more astute people on this thread pointed out...we weren't there. They could have thought she was headed to the bathroom, or to put some clothes on, or something.
I wouldn't want to deal with a crazy, knife wielding person at a range of 2 to 5 feet. That's inside the average person's reach. Knife fighting range. Likely explains the five shots, as well.
IMHO, the one cop who *didn't* fire because he didn't have a clear view of the situation, is the key. Says to me that this situation went to hell in a hurry, and everyone present was forced to react quickly. *IF* they'd had plenty of time to take an aimed shot to the leg, or use a taser, or throw a net over her, or some of the other more asinine suggestions on this thread...the fourth cop would have been right in the middle of it. But, I wasn't there....
Its really kinda sad, we see case after case where the cops are called to help someone and end up shooting them.
IMO its how they are trained.