How does someone get out of a non-disclosure agreement?

My sister signed a non-disclosure agreement which stated she may never to speak to anyone about a certain event. This was put forth by an attorney representing a client who was responsible for the event. My sister signed the NDA and was given a small sum of money for doing so. The event was traumatic and the statue of limitations has run out. My sister contacted this attorney saying she wanted to pay back the sum of money and be released from the NDA. The lawyer sent her an email which said, in essence, that if she dared to make the attempt to pay back the money in order to get out of the NDA, she would be swiftly and harshly penalized for far more than the money she would send back. This sounds like foul play from start to finish. Is there anything that can be done?