Hilary can't win. There is a full bag of dirt ready and waiting for her. She'll never get her approval up from where it is now, but it could still slide down. Just remember how ugly it got against Obama, and he wasn't trying to (metaphorically) shoot for center mass, just wing her enough to bring her down. A Republican opponent will not provide the same courtesy.
Elizabeth Warren is an interesting choice, and she's already shown a great gift for conflationary oratory. Her biggest argument so far has been for student loan interest easing, citing that it's wrong to make money off of students while they go to school. Unfortunately for her argument, students aren't charged interest while they are students (i.e. workers in the workforce are charged interest, not students) on a large portion of their financial aid; specifically, Pell money is a gift and Stafford subsidized loan interest is paid by the government while the student is in school. Realistically, if you can't attend school for under $15,000 a year, don't apply for scholarships, and refuse to work at least part time, you simply don't deserve the unsubsidized Stafford top-up. Basically, what I'm saying here is Warren is already pushing junk arguments at the lower class in an attempt to bribe them with at the minimum good intentions and at the maximum a bunch of public money. But she plays well for the cameras, so, whatever.