You know what? To many of us here, including me, the scene with Marla's gun seemed like a total cringe. But now, having replayed it, I thought: we don't know exactly when she started therapy with Amber. Was it after the accident or did she have it long before and the accident was just an addition to the problems she's already struggling with? And if the latter is true, maybe something happened to her, because of which she carried a gun in her bag every day? It may even be related to Bella's accident in her past since Marla and Amber are old friends. And this incident, as we know, was of a violent nature. If these assumptions are correct, then her reaction to MC's muttering to himself that it's better for Vic to die doesn't seem so unexpected and exaggerated anymore, right? She is really scared and in a panic, her past incident and the present situation are mixed in her head, and she thinks she is protecting Vic from an attack.