(re: Thieves in QfG2) I’ve had the same problem too in a recent replay.
1. You must show her the sign on the first day. Someone told me you can do it on the second, but it didn’t work for me.
2. Keep visiting her each night. More than once. Once when the night is young, then at the middle of the night, etc.
3. If you can’t get it before the 3rd elemental then you HAVE to restart.
I replayed the game myself 4 times with my thief just cause of that bug…