Did you select the quest for the promotion? If it's not a promotion bug, then it doesn't really matter if she's there or not. I do know they sometimes don't appear if they're your first mate, but that's all I know.
If you have a lot of companions more than 15 let's say. Unless they are available for promotion or they are your first mate they may not appear because all of your companions can't be in the tavern cellar it would be too crowded and there are no spots to place them unless you want it to look uneat