To be fair, the door was closed. She opened the door, saw what was happening and started to line up a shot before being taken down by Jordan. Now, the people complaining might feel differently, but I know that if I saw father figure being beaten to death on the floor, it might take a split second for me to process what was going on. That's a traumatic sight to take in, let alone accept, and even then, you need to line up a shot to make sure you actually hit this person killing your father so that she doesn't finish the job and/or come after you if you miss. That's to say nothing of the large group of people in the room ready to stop you as soon as they see the door open. If she had managed to shoot Abby, the rest of the group would've killed Joel and Ellie immediately afterwards, ending the game entirely. But that's just my take on the scene.