which again makes me think..Tia can obiously see the origional future and all you have to do is look at how Will feels at present towards pirates and how he will behave towards Bekett when Will takes up Liz's dads place.
In my opinion Tia can sense the emotions the characters feel at that very moment in time..as in of the present..so she must KNOW that elizabeth loves Jack deep down..and if they get together she will fall for him..and right now she knows Jack is basically infatuated with Elizabeth so she knows she can use it to her advantage..I dont think she can actually tell or know for sure how the characters wil certainly feel in the future..she's just guessing based on what she knows about them allhow things COULD play out.. in her own little version of the future she is trying to create.