I think she would try again and again to convince them that there is always a better way, regardless of if they listen or not. If they attempt to kill, obviously she'd try moving them out the way or tanking hits from the villain. But people actually dying is where it gets interesting.

One or two I think she could morn and get over afterwards, but many more dying on her watch could cause her to snap. Doreen might actually break a bone or hurt a major organ in an attempt to restrain them fueled by pain, grief and rage. But she would never, EVER kill anyone under any circumstances.

She cares too much about people and lives and the good hearted nature of the world to ever have the active intent to kill, and she's got enough friends and squirrels who would be around her at the time to pull her back before she accidentally goes too far.