My daughter in law passed away in March of this year. Her 15 year old daughter (will be 16 on July 3rd)has been living with my son and her mother since she was 3 years old. My son was not able to adopt her and now her biological father insists that she spend every other weekend with him and if she misses 1 weekend she has to spend 2 weekends in a row with him and his new family. He does not pay child support for her since her mother passed way, only has her medial and dental provided. Can she tell him no? Or does she have to go with him? There was never a divorce because her mother and biological father were never married and therefore there was never any legal custody or visitation rights set up.

What can she do if she doesn't want to go?

?? Who has legal custody of the child, * if anyone* since a step father that has not adopted does not have any legal rights to keep and raise the child what so ever.

And normally the grandmother will not have rights over the bio father.
So to be honest I doubt if any of the visits are court ordered and if they were it would have most likely been the mother.

So it may be that the bio father could easily go and get custody the child if he wanted to. Can he legally do the demands, most likely not, unless it is written in the custody agreement.
And sorry divorce has nothing to do with custody and visitation, that is done for any child where the parents are not together.

So it appears bio father could go to court and get the child full time with the steop father not having any visits what so ever.