Overall a very good episode with an amazing performance by Stana but the PTSD got "resolved" way too fast just by talking Esposito who's been through the same. I mean it was not gone but going from total breakdown to functioning member of the team went by way too fast.
I don't know... in my own experience, sometimes the difference between being totally overwhelmed by a situation and being able to cope with it can be just a matter of pausing, calming down, taking a look at your own reactions, and finding a new mindset to approach things from. A conscious shift of perspective, both about the situation and your own reaction to it, can make a lot of difference.
Besides, by now Kate's had months of therapeutic guidance from Michael Dorn to draw on. But she wasn't really ready to listen to it before. I'd guess that maybe seeing herself break down like that was a wakeup call, and once Espo's talk helped her refocus and decide she could cope, she already had some guidance as to how, and it was just a matter of finally believing it and applying it.