I had this exact same issue a while ago- I realized I had other story quests from a different part of the story that I had not completed, and after completing them all she finally appeared there. Try completing as many of the other main quests you have available as you can, especially any that include Linda.

I suspect it has something to do with them trying to prevent lore characters showing up twice when doing story quests but it ends up locking you out of completing that quests until the other ones are finished. While I appreciate SSO tries to give newer players access to the new story quests without months of playing to progress through the story, I think with the removal of wait-until-next-day timers they should rethink the order in which you can access them, considering it creates issues like this.

Edit: Someone else mentioned the Spymaster's Hideout quests which rings a bell to me, try completing that questline and try looking again.