I think that Theresa's grand plan is simply to make sure Albion survives, I mean she can see the future so she would have foreseen the crawler (and possibly some other more powerful creature of darkness), but she would probably have seen it/them destroy albion, so she needed the Spire to know how to stop it/them. And if there was a more powerful creature of darkness then I reckon/hope that Albion is going to get dragged, kicking and screaming, back to the age of heroes and magic. So I think the whole series might be connected like this Fable(TLC) as setting up what it needs (Theresa, Heroes, Albion and possibly the 'supreme darkness'), Fable 2 as Theresa's preparation (i.e the spire), Fable 3 as surviving the first attack (and making sure Theresa's pre-spire visions didn't happen), Fable 4 as a battle that ultimately destroys technology and Fable 5 as the final battle and the return of the Guild