I have never played Fable I, though I have done research on it lately and I completed Fable II (in less than three days might I add?) I started doing research on July 20th 2009. And I find it obvious that Theresa was the sister of the main character in Fable. Even though I do not recall the first time Theresa told Sparrow she was blind (I did not discover this until I started my research). And only recently doing my research did I make sense of the death of Rose (Sparrow’s sister).
I also find it obvious Theresa is evil as in she did not want to help Sparrow at all, but needed her to kill Lucian for her so she could gain control of the Spire. I am worried Theresa will be worse than Lucian because she has more knowledge than he ever did. I am guess she had the same thing happen to her that Garth had happen to him a little after Sparrow defeated Lucian. Garth had me defeat someone and he got much power after that.