Yeah, in my case Jaheira automatically permanently left my party after I killed Ketheric every single time and I tried everything. But she then magically appeared in my camp and I can talk to her and shit and the game thinks she's part of my crew but when I ask her to join my party nothing happens. In other words I can't complete any of the quest lines involving her.
Its different to your situation but I think Jaheira as a character is completely bugged atm.
I´ve found a workaround from a user called "Lazy Spartan" in the SteamForum (watch the video linked below) At least I can continue to play without loosing Jaheira now...
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Lazy Spartan [besitzt Baldur's Gate 3] 12. Sep. um 18:10 None of the suggested workarounds seems to work for me. This one did:
Toggle group mode Send Jaheira through the portal Send another character (Other) than your main (Tav) through With Other; talk to Jaheira and get her to come with you, but go to camp Send Tav through the portal Use Minor Conjuration: Create Water on the brine spill on the stairs Go to camp with Tav, talk to Jaheira and get her to join your team
Unfortunately, Jaheira still has very low approval. This might be risky playing on. I recorded how I did it here if it's easier to follow:
