If waiting to tell her until the fall means stringing her along…then no. Tell her now. It’ll suck, but if you’re not feeling it, you’re not feeling it. She’ll only be more humiliated and hurt if she finds out you’ve been “faking it” for the past few months. Be honest.
But, also, make sure you’re not being too hasty. Long distance messes with your head. Are you absolutely positive that when she comes back, you’re not going to have feelings for her still? Will you regret making the decision to cut things off?
You’re in a tough spot. Honesty is the best advice I can give you, but don’t rush into anything because this is the kind of thing you can’t ever take back.