Can a mother take a child away from the father without a valid reason in Mississippi?

I'm asking on behalf of a very good friend. He is currently still trying get his divorce final, and has been trying to get the mother to sign the divorce papers the last 5 months and she keeps putting it off. Neither of them have the money to pay for a lawyer, so they are trying to settle this themselves since it is less costly. The mother of their child does not like me at all, and it's because he is friends with me, she is threatening to take his son away. Can she legally do that without a valid enough reason? I have never put the child in danger. I've watched both of his children without any problems what so ever, and I'm great with kids (I used to work in a day care, and the kids and parents loved me), she should not have any reason to threaten him and use his child as a pawn to control him, just because he and I are friends, right? I do not do drugs, nor do I drink, or go out and party, nor have I threatened or put them in harms way at all. Any help or advise would be nice. I do not want him to lose either of his children. They are the most important people in his life. But I do not believe she can take his child away without a valid enough reason. Just because she doesn't like me, and doesn't want me around the children when he has them for the week. They go back and forth between the mothers and him every week. One has a court order and they have joint custody, but the soon to be ex wife, is constantly trying to use their child as a pawn.