Apparently Bethesda has warned us that completing the main quest before doing anything else, breaks some quest lines. In my girlfriends game, she can no longer complete the thief guilds quest line due to someone we need to speak to having a different position.

Now i understand to have an evolving game world some quests should become available and not available. How ever as the thief guilds is one of the major quest lines in the game, it's a bit disappointing that this isn't made known.

Is this actually the true? or is this actually a bug that shes been unlucky to encounter.