Child Custody 2 years after divorce

My daughter has been divorced for 2 years, and she and her ex had a seperation agreement that had what they thought were fair visitations with their then 2 year old son. Now, 2 years later, her ex has decided that he is going for full custody, since neither of them actually have legal custody. Their son has lived with my daughter and her new husband and daughter for 2 years and has spent every other weekend and several vacations every year with him. He has been texting her with hateful things, like “I am going to court and am going to get full custody and you will never see him again” and “I have talked to a social worker and you can expect them to show up at your house”. My question is, can these texts and others be construed as harassment on his part? She is a nervous wreck and is afraid when he picks their son up next weekend that he won’t bring him back. She is willing to go to mediation but her ex has said that mediation will not work because he is going to get full custody and no judge will ever give her custody. What are her rights and what should her next step be when dealing with someone who is obviously a verbal abuser and has so much hate for her, and obviously isn’t thinking about the best interest of their son like she is?

Your daughter should consult with a lawyer, and file for emergency custody. That is not acceptable behavior on her ex’s part.