Jaheira's romance by all accounts is tricky. Part of the romance scripts are triggered by events, others by time (game time as well as real time). If it's of any comfort, I managed to start the romance but somewhere I must've said something wrong 'cos thr romance variable is 3, which means it's dead.
Did you get summoned before the Harpers (Galvarey)? I believe that's another important trigger.
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"Butt-kicking for goodness!" - Minsc
"Cities always teem with evil and decay. Let's give it a good shake and SEE WHAT FALLS OUT!!" - Minsc