I know that a lot of people want her to gain Molecular Manipulation. I'm not one of them.
This is my view on the power (Reposted)--- I dislike this power, all the powers within it are basically cousins powers. There is nothing new, because anything one power can do, three others power can do. The only difference would be the results (ie) stronger or weaker. This is where Piper powers are heading, with her ending up with many cousin abilities.
Personally, I don't think Piper need many powers or even Molecular Manipulation and all the crap powers in it. She just need one solid great power with abilities within it (ie) empathy or telepathy.
My pick is Super Speed. I would then evolve that power so she could use Invisibility (she would be able to vibrate her molecules and make herself invisible. Next ability is Intangibilty, again moving her molecules to move through solid objects.
Now, what power would you give her and how would you evolve it?