There was bug with original game where, sometime, after you defeat Gromnir, Melissan wouldn't show up (which she is supposed to do). I think the Patch...
http://www.bioware.com/games/throne_...patches/#patch
... fixes this. But if it wasn't that try the Baldurdash FixPack...
http://members.rogers.com/mrkevvy/To.../TOBfixes.html
The bad news is that if you are already past the room where you killed Gromnir & Melissan didn't show up at the time, you have to restart, although next time you get there (after installing the Patch(es), of course), you won't experience this problem again.
- Imrahil