You should be able to "train" her exhibition level at this point, I did it not too long ago and was able to get the trait. Go to her room when she is not working "Knock on the door" and not "talk" option, than one of lower options should have (+exhibition) on it, pick it and than in the scene you have to pick last option "lewd", it will rise the stat, do that 10 times, get the trait and option will be unlocked.