It’s not right. Her action didn’t harm you, probably won’t ever harm you. But I would imagine that your respect for her has taken a nosedive. I know people aren’t perfect, and we need to accept imperfections or we’d have no friends, but really, do you need this person as a friend?
I don’t think that informing her colleges would be the appropriate maneuver. Simply posting your essay on the internet might wind up with some schools finding it, and rejecting her for plagiarism. You could post it on this website, “Here’s the essay that got me into …”
But probably, the most direct and honorable thing to do would be to simply sit down with her and say, “Look, I know that you copied my essay. That was wrong. Do you realize how wrong it was? I gave you access to it to help you, to lend guidance to your creative process, not to be a substitute for it. I think that you should redo your Common App, write your own essays, and submit that for any further applications. I don’t know what you can do to fix the ones you’ve already submitted. Do you have any ideas?”
I suspect that her reaction will tell you a lot about her character and the future of your friendship. Just out of curiosity, did she apply to any schools that you had applied to? Didn’t it occur to her that an admissions officer could recognize the essay?