I've finished 4 playthroughs, including Tactician and Honour Mode. In every single one of my runs, I was able to recruit Jaheria. After you beat Ketheric at the top of Moonrise Towers, you have the option to ask Jaheira to join you at the Mind Flayer Colony, don't. I normally already have 4 party members so she cannot join. After you beat Ketheric/Myrkul at the end of Act 2, Jaheria will be in the Throne Room before you venture to Baldur's Gate. You have the option to ask her to join you in Act 3. When I recruit her this way, she always appears, can join the active party, and I am able to complete her missions without issue.
There was also a post regarding this on
Steam:
Nyaria has Baldur's Gate 3 Aug 21, 2023 @ 1:36am
It's a weird bug, no idea what triggers it, easiest way to avoid it is to not bring her to fight Ketheric, kill him without her, and then recruit her after the battle because she will be eager to join you after, and it completely bypasses the weird bug.
My suggestion is, don't bring Jaheria to the Mind Flayer Colony, kill Ketheric, then try recruiting her in the Throne Room. See if that helps.
