Unstable ex-husband's girlfriend

Here is my situation - my ex-husband is living with a woman who lost physical custody of her children within the last year. She refused to provide the medical documents requested. I am concerned for the safety of my children when they are with him (and her). Are there any cases involving a similar situation where the father's girlfriend is unstable - therefore, a custody change decreasing the amount of time spent with the father? How can I protect my children?

Yes--you can show the court the problem she had and get an order that she cannot be around, or that he cannot have visits if she is there.