Why is this a possession of marijuana charge, and whats going to happen?

I was caught with a grinder in my car, that honestly, was NOT mine. My friend left it in my car, and I told the officer it was my friends, even though they must hear that all the time.....The grinder also had no weed in it. I went to court and the judge said I was charged with marijuana possession, so I postponed to get a lawyer for next time. If my friend comes into court with me next time, and admits it was hers, NOT mine, will the charge get dropped for me? Also will it then be passed on to her?