What she did was wrong, yes, but what you did was also wrong. It's not about a tit-for-tat, she grabs your penis so you grab her breasts. I understand why you may have reacted like that, but the fact of the matter is you touched someone without consent. That is a violation, even if it was in retaliation to her doing the same to you.

You always, ALWAYS need to practice consent, in general, yes, but especially in regards to someone's physical boundaries. You have the right to defend yours, especially if they are violated, but the answer to such a thing is not violating someone else's boundaries. Defending yourself appropriately would have been telling an adult you could trust, since you are a minor. They can help you process your feelings about what happened and take the necessary disciplinary steps to keep such a thing from happening again.

I am sorry this happened to you, but remember, consent is key, and just because someone violates yours doesn't mean it's appropriate to violate someone else's in return.