It's WoLmond verse, so L'sta is traveling with Almond and the Ilsabard Contingent to do the whole Garlemald part of the MSQ story.

If I'm remembering right, Aidan is the third in command of the Xth legion who contacts the contingent to surrender with his part of the legion. L'sta is sent to escort them back to Camp Broken Glass, but they're intercepted by a section of Aidan's men who refuse to surrender - Aidan negotiates them taking himself and L'sta in exchange for letting the rest of them go, since the rest of them aren't the ones the loyalists have issue with (it's mostly Aidan for surrendering) (it's not very logical they'd only have beef with him, but story needs what story needs).

Soooo... Aidan and L'sta end up captives until they're eventually freed, in the interim the whole Drugging Thing happens, but you already know about that hahaha.

AS FOR THE TRAUMA...Aidan's honestly fine with being around L'sta. If anything they ended up being a weird sort of friends after it, actually (like war buddies, but, y'know, noncon drugging). They both sort of opt not to talk much about it, for better or worse.