Jaheira's romance is reportedly buggy, even post-patch. Numerous problems have been witnessed - including slow progression such as you seem to be experiencing.
It's strange that you haven't been able to at least find the poisoned man, every time I have played that has happened the first or second time I ventured out from Athkatla. Are you sure you didn't miss him?
I currently have a game going in which my protagonist is romancing Jaheira, and I haven't had any problems so far. Most romances do not take place within the city, and I know that Jaheira's Harper Quests also do not. They also are supposed to operate on real-time (not game-time) so sometimes leaving your game running for an hour or so speeds things up, as does leaving the game paused. Other times there's something you actually have to do in the game - a related quest or what not in order to get the romance to progress to the next stage. For instance, if you haven't started Jaheira's Harper quests, that might be what is holding up your romance currently. Unfortunately, I'm not too sure whether or not you can even get the Harper quests without first rescuing the poisoned man. Is Xzar present in the Docks District? If so, try talking to him and getting that quest.
Dropping a romance candidate from your party also ends whatever romance you'd started with that candidate. This includes petrification in Jaheira's case(as petrified members drop from your party automatically).
You can either use the CLUA Console (or an editor such as ShadowKeeper)to reactivate the romance, or you can download an unofficial patch that is supposed to fix many of the problems (script errors) related to the Jaheira romance
here. I'm not certain whether this patch will fix your romance once it has already been triggered, but it's worth a try.
You may want to patch, leave Athkatla, and see whether or not things improve for you, and then reactivate the romance if nothing changes. If that doesn't work, you may need to use CLUA to create Renfield - it really is strange that you haven't run into him.
[ 01-10-2002: Message edited by: Erydian ]
[ 01-10-2002: Message edited by: Erydian ]