Hello Purple. I've been in situations like that where I've felt uncomfortable and left. For me sometimes afterward I've felt very badly about myself that I left, as I think I could have handled it speaking with them. Leaving was a gut reaction.

It may have worked out to the advantage of both of you if you had stayed and talked. If you feel that is the case there is nothing wrong with waiting for another opportunity or maybe even bringing it up.

However the most important thing is your own comfort. I say this especially because your issues are different than mine especially I do not suffer PTSD so I can't imagine what might trigger that or be a problem for you.

I say keep yourself safe first and if that means keeping separate then that is OK and no reason for second guessing or guilt. You do not owe her just because you share something but you do owe yourself to keep yourself mentally healthy.

That is just my opinion and I'm hoping others will chime in to support or disagree with me... Maybe point out something I haven't thought of.