I'm going to see if this can be talked out for now, but I would like to make sure two points are clear:
1) That is, in fact, a rock, and not a grenade. So it's not a matter of would she actually do it, it's a matter that she can't do it.
2) Shell Shock is also a heavy drinker. Sober, shunning may be no big deal. Aftera pintseveral pintsa barrela lot of alcohol, that may not be the case. I can see how Grif can make him feel regret if he so chooses. Though not the "oh no I killed a bunch of stuff" regret, the "oh no, my friends don't like me and I have no idea why" sort of regret.
I'd bring up other points, but I'm interested to see where you'd want to take Shell Shock after the heist, and I don't want to pre-emptively influence that answer. I'll be watching the conversation closely, and keeping the DM hat on standby in case things get too heated/frustrating for all involved. I think I speak for everyone when I say I'd much rather see this resolved without having somepony feel as though they want to give up on a character.
*juggles hats*