My suggestion is that you consult with an experienced family law attorney, as more than her threats of violence toward you would be necessary. Custody cases are complex and fact oriented. There are what is known as the "best interest factors" which the court examines when there is a custody dispute. Domestic violence is only 1 of 12 factors. Was this a child born out of wedlock? What circumstances have changed since the award of custody, other than the threats of violence? Your involvement in the child's life is also important, as well as the child's age. The fact that she's made threats does not mean she is an unfit parent. Has CPS ever been involved? Far, far more facts needed to be disclosed/explored in order to properly assess your inquiry.
Neil M. Colman
Mr. Colman is licensed to practice law in Michigan. The response herein is not legal advice and does not create an attorney/client relationship. The response is in the form of legal education and is intended to provide general information about the matter within the question. Oftentimes the question does not include significant and important facts and timelines that, if known, could significantly change the reply and make it unsuitable. Mr. Colman strongly advises the questioner to confer with an attorney in your state in order to ensure proper advice is received.