Hi, anon! It was a really great observation, I’m so happy you thought of it! And I know, I’m trying to not let myself sink too deeply into that, but it’s simply canon fact that without even knowing the halo would kick in, when Ava saw Beatrice under threat from a GUN, she RAN TOWARD IT with no intention but to interfere somehow even if that meant putting herself in harm’s way.
It was in fact the halo that surprised her (and all of them) and saved her from jumping straight into the path of the bullets. She’s hardly at the stage of (near) invincibility where she’s going to instinctively seek out that kind of damage, even if the halo HAD been able to absorb that kind of damage, she’s not nearly at that point yet, this was just her.
And the person she did that for is Beatrice. Sure, maybe it’d have been for anyone. But it wasn’t.