There are a couple of things that act as "stoppers" with Erynn (besides Emily
).
One is Erynn being afraid of what a relationship will do to the friendship, she doesn't wanna lose him as a friend, she's happier since he came back, so she's scared to change their relationship, she's scared that entering a relationship will lead them apart in the future and change their friendship.
As for trauma, i don't think traumatized people know they're traumatized, and when told that they have issues they deny.
It's just something that hits them... not something they counciously think about.
The events that happened with Zane-Ethan did scar her, and often leads to her freaking out when we get intimate, but i doubt that is something she's actively thinking about.
The MC does a "meh" job getting her to feel secure enough for a relationship, they stay in that friends that sometimes fool around area that scares her, he never says anything besides "we will take it slow".
Stepping up the relationship when Ethan is dealt with is a very traditional structure, think of a quest line in an RPG, the Erynn is the quest giver, Ethan is the problem you have to solve and you get the "reward" after you solve the quest.
Getting rid of Ethan will be a big boost for Erynn to get over her issues and of course trust the guy that solved her problems.
And goes without saying send Emily to Europe for a month, that will help more than anything.