Not everyone who is in combat experiences PTSD (Though I don't know what the percentage is either. Not even ballpark).
I can't speak for international statistics, but in the US, statistics are very mixed. I've seen some articles saying as many as 1 in 8 returning soldiers experience PTSD.
The actual US Department of Veterans Affairs estimate is as follows:
The U.S. Department of Veterans Affairs estimates that PTSD afflicts: Almost 31 percent of Vietnam veterans. As many as 10 percent of Gulf War (Desert Storm) veterans. 11 percent of veterans of the war in Afghanistan.
Combat is also far from the only thing that can trigger PTSD. Car accidents. Assault. Sexual assault/abuse. Threats. Witnessing violence. Etc.
But yeah, I'd agree. At this point while she's clearly been touched by war and the awfulness of it, we don't know enough about her mental state and what happened between TLJ and Dreamfall to really say it's PTSD. It's possible. But like I said, Mental Health problems tend to group together and sometimes the lines between them are less distinct than people want to believe.