Plus, sometimes people just get angry and act in strange, irrational ways. Or lash out for no reason. Especially when it's the end of the freakin world. I hardly expect everyone to be charming and likeable in that situation, and find it strange that somehow fans expect that she should be.
I agree with this, admittedly as someone who thinks the character is written very badly. The problem for me is that in a world like this one, most people would be off their rockers by now - wildly inconsistent, irrational etc (with the fact that nobody will have their meds anymore being only a small part of it). Yet narrative - actual story - needs to be consistent and organized and coherent; it can only pretend to be chaotic or it loses the audience, who need the comfort of narrative organization.