I know it's not exactly the same situation, but I've been in one similar.
When I was married, my husband and I were moving from one house to another. While trying to load the last few boxes in the back of my car, so I could finally call it a day, I accidentally broke a collectible football helmet he owned. After becoming completely unglued, my husband jumped into the car and sped away, leaving me alone in the driveway. Soon, he came back and I thought he'd calmed down enough for it to be safe for me to get into the car with him.
I did, and as we drove away, he began to scream at me. Then, he pulled over and started hitting me. I managed to get out of the car and run for a few feet, but he caught up to me and dragged me back to the car by my hair, kicking me the entire way. A few people drove by, and one man in a truck slowed down, but I screamed at him to get the hell out of there. My husband was in a bad mood, and there is no limit to what he'll do to somebody when he's in a bad mood. He would have killed somebody who tried to help me, and I would have felt guilty over that for the rest of my life.
Anyway, the point of all this is I can honestly say that, as a victim, I would not want somebody to put their life in danger trying to play the hero with a crazy person. I think what this lady did is exactly what should have been done. If she'd tried to help or intervene, it could have been a lot worse than what it was.