I would think her being on the Normandy for good after the Expansion would be a good possibility as well.
She has no reason at all to stay on Illium after the SB situation is resolved.
For the people who didn't romance her (how could you

), she could be on the ship because of her expertise.
For those who did romance her (all of us, lol) she would be there because Shepard loves her and She loves Shepard (and well love her as well)

.
She has even said that she wants to come with Shepard but can't because of her situation.
So, logically, she would stay on the Normandy after as a non-playable squadmate until ME3, where she would be a squadmate.