My experience is that even though Lae'zel was abducted, Yenna disappears as soon as the conversation with Orin happens where she impersonates Lae'zel. I could try going back to the point before Lae'zel was captured and long resting a few times to try and get the scene where Yenna and Lae'zel face off to trigger, but that's 20-30 hours ago in my PT. I filed a bug report hoping Larian brings Yenna back. I just worry Grub will miss her.
In my playthrough, after you see through Orin she will release Yenna and mock you after passing the dice check. You then have the option to talk to Yenna afterwards and she's super freaked out and says she will never be safe. Then she's totally OK the next day and offers you soup. Grub never gains any new dialogue.
I think they ran out of time to develop Yenna or assumed that because for many players she will be the one chosen or lost, they just didn't bother to build her up as a character with any real conversation. I had more conversation with some girl at the cemetery in Act 3 than I did with Yenna, it's crazy.
