Given the facts here, it seems that you were harassed by the landlord and that the person who rented you the apartment did so illegally. That would negate a leg for her to stand on. Further, in order to have Fraud or Forgery, you would have to intend fraud, or sign papers in someone elses name.
It would be a weak case, but you can actually sue her for fraud if she told you she had the right to sublet the apartment. Cancelling the check was not illegal as you did not receive the consideration that you expected for the money you paid. You are mitigating your damage.
While nothing takes the place of advice you receive from a lawyer of your own, and while the comments above do not constitute legal advice, I think you can sleep easy. If there is a problem, say nothing to anyone, and contact a lawyer immediately.