How serious is a simple assault charge in nj?

I let a girl stay in my home while she went to school and she slept with my boyfriend. We argued and I kicked them both out of my house. I saw her the same night in a laundrymat and we argued somemore. She called the cops from the laundrymat and said I threatned to stab her with scissors and I pushed her down some stairs. She kept changing her story when questioned and there was no arrest. A couple days later I receive a summons for simple assault and theft of services. I never touched her or broke any of her property now the state or city is calling me to court. How hard will it be to beat? Should I go woth a legal aid?