How do I prove my innocence on a criminal mischief charge without getting an attorney?

I was at my friend’s house and she was very upset saying that her cousin had keyed her friend’s car when it was in his driveway. Then she had asked me to take her to his house so she could talk to him and clear things up. When we had gotten there, I told her that I did not feel comfortable parking in his driveway just because of the simple fact about him previously keying her friend’s car so she took me to a road around the corner where I could park. Then she wanted me to walk over with her for moral support and so I had agreed to go with her but I had said I would outside for her while she talked to him. When we had walked up to his house she ended up running over to a car in the driveway and started keying that car. I was yelling at her while still standing far from the car but when I realized she was not listening to me I had started to walk away being that I wanted nothing to do with it. While I was walking away, I heard two people screaming, her cousin and his girlfriend. It ended up being his girlfriend’s car who I have never met even to this day. I got lost walking back to my car and when I saw an officer driving by I had walked up and asked him to help me find it but he in turn arrested me saying that I know what I did. They had taken me in with her accusing me of also keying the car, which she had told them I had nothing to do with. We are scheduled to go to court in a week and I have a summons for criminal mischief. I do not trust my friend anymore because she put me in this situation. She is struggling to come up with the money to pay for the damages and so what if she ends up switching up and blaming it on me? I did have a friend officer make her put in writing that I had nothing to do with it in case it would come in handy. I do not have anything but a few traffic tickets on my record and I do not have the money to pay for an attorney. I am completely innocent, what do I do?