I have inspected Jaheira's escape script and found a potential loophole. She might not be available if you had talked to her in Chateau Irenicus at least once.
Triggering her appearance is a bit complicated. Try this chain of actions when you are in the Docks District. Simply copy and paste the whole line into the debug console and press enter:
C:Eval('MoveGlobal("AR0300","Jaheira",[1257.3007])');C:Eval('ActionOverride("Jaheira",SetDialog("JAHEIRAP"))');C:Eval('ActionOverride("Jaheira",SetGlobal("KickedOut","LOCALS",1))');C:Eval('ActionOverride("Jaheira",SetNumTimesTalkedTo(1))')