So as much as you're right to say that, I can back up my point of view just by telling you that so far, we haven't slept with Jill yet. Knowing that a letter to our mother is probably waiting for us in the next episode, there is a good chance that we will find out about the family relationship between Jill and Lynette and finally MC will eventually stop all relations with her. (You are right on this point, DPC don't like incest, so as the MC with his big morality)
Which will make our choice about what we think of tommy a big influence on whether she ends up with her.
She's going to be there, the great frustration of this game ^^
By the way, sorry if my english seems to be bad. I am a french guy with just the right level of English skills to play the game without translation ^^