Bump. Happened to Jaheira in Act 3. I believe it was triggered by stealth mechanics interrupted by a cutscene. Working save is so old now that I may just take all her good kit and leave her at camp. Tried many different suggested workarounds:
-Dismiss, long rest, re-add
-Dismissed entire party, long rest, re-add
-Fast Travel separately, re-group
-Unequipped eeverything, re-equipped with different gear just too see if there was an item involved
-Etc.
I've just read in other posts that there may be a way to workaround the issue with various combinations of ending all companions turns in turn-based mode, group stealth, etc. so I might try some of those later before I just give up on Jaheira.