If you're 100% sure that nothing you said to her was sexually inappropriate or that you used your professional power (if you had any over her) to put her in an uncomfortable position then you'd be wise to seek legal counsel immediately.
This isn't to say that anything can be done from a legal perspective, especially if you're in an at-will employment state.
Unfortunately with these situations, a rule that's put in place to protect workers can also be abused. That being said, it would be really tricky and unethical for a company to fire an employee for sexual misconduct (I'm assuming they're claiming sexual misconduct and not run-of-the-mill misconduct) without a thorough investigation and proof of the allegations.
If they don't have these things against you, you likely have a better chance of pursuing legal recourse against the company for wrongful termination.