You will need to wait until you receive exoneration in the criminal case.
In virtually every state, statements made to the police/authorities in a criminal case (and particularly those in court) are absolutely privileged. This means that you cannot bring an action for defamation or anything else based on those statements.
However,once exonerated, you can bring a malicious prosecution/defamation action against the complaining witness (in most states) if you can PROVE that her statements were knowingly false, and were intended to harrass you or deprive you of your rights.
It is VERY difficult to prove these cases. Winning the criminal case is not nearly enough (reason: an acauittal only means that there was not enough evidence to prove you guilty beyond a reasonable doubt, it does not mean you are innocent, it does not mean that ex was lying, just that there was some "doubt" that you were guilty).
You should think long and hard before you go down this road. Few reputable attorneys take these cases (rarely successful, and even if successful, how much is case worth -- if you could win a big judgment, could exgf actually pay tons of money? Enough to pay lawyer?)
Remember, this is merely an overview of various jurisdictions. Laws in your state may differ, and you should consult an attorney licensed in your state, as only a licensed attorney may provide legal advice.