The way I see it, Obama has wedged Hillary into a corner here. She has come out against TPP and has been accused of flip-flopping for it, but she has also run basically as Obama's third term. I don't see her being able to manuver between the issues on this, but I might be wrong; she might just not get called on it.
She'll probably come out in support of it after the primary. It hurts her image because she's clearly flip flopped on this (and may even do so again) but I'm not sure how much people care about the TPP.People care about it a great deal. And more will care if Trump makes it a talking point. (Sad but true.)
If she flips on the TPP after winning the nomination, I WILL NOT vote for her, no matter what. I suspect that it will be the proverbial straw for many on the far left. (And she's going to need those votes, I think.)