It sounds to me that you know where you stand on your values, and you know how to make decisions to support those values. As you do more things and make more decisions on your own, your mom will likely come to see that you are growing up and are able to negotiate adult issues in a way that won't derail your academic goals.
I would let the topic rest for now. Once you are accepted at a school and waiting for move-in, you may receive material in the mail about Greek Life. That might be a good time to approach the topic again.
It's funny how knowledge of one bad experience can turn a person's entire point of view. I would think that in light of the many successful college grads in the world who are Greek, one horror story wouldn't hold quite so much weight.
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Good luck!