Allison had already figured that he would probably shoot again the second he heard her attempt another Rumor, but when she catches the way he taps his ear, she knows that they're screwed. He had come prepared. Even if Five could somehow go back further in time, if she could wait for him outside of the barn, she wouldn't be able to stop him. Not in her usual ways, anyway.

"No." Her voice wavers, but she tilts her chin up slightly, defiantly. By stopping Vanya she knows she screwed herself over, because now Five also can't shoot him since it would be interfering, but what else would there be? Vanya had gotten shot - killed for trying to interfere. If Five would have tried, or Klaus, or Diego, or Luther... She can't lose them. She can't lose any one of them, which is why she had done what she did.

She steals a glance at her siblings, at the silent desperation that mirrors her own. I'm sorry, she wishes she could tell them. I love you.

She wishes they could have more time, that shit hadn't come to this.

There's a brief moment that she looks almost defeated, as if her resolve is broken and she will give him the answer he's expecting, but instead of speaking she charges towards the Swede instead, ready to try and keep him from shooting her siblings. Ready to do whatever she can to save them, because she refuses to lose any of them again.