While I typically recommend that people consult an attorney in their jurisdiction, since laws vary by state and what might be right here in Washington might be right in KS or PA. However, your daughter will not lose her parental rights simply by letting her daughter visit her grandparents. The grandparents may be able to request visitation--Washington used to have a law allowing that, but it was ruled unconstitutional, so now grandparents here have no right to custody or visitation whatsoever, but other states may have different provisions--but they can't take away custody unless they prove in court that she is an unfit parent. Parental rights are constitutionally protected and easily terminated.
If there is reason to believe that the grandparents might try to do this, post your question to Pennsylvania attorneys. Usually only a court in a child's home state could make a ruling about custody, so it is unlikely that they would be able to do anything just because the child is there visiting, but there are generally exceptions available for emergencies.
In my opinion, though, if your daughter and her in-laws are so mutually distrustful that there is a chance they would tell a court that allowing the child to go back to her mother would put her in immediate danger, it might be a better idea to simply not allow the child to visit them without her mother accompanying her.
Some persons go to court and make up all sorts of horrid allegations against parents that later are found to be untrue.
Unfortunately for the parents, the judges can act only on information available to the judges.
If someone goes to court and declares that the mother uses drug, does not have the money to raise the child, and beats up the child, you can be certain that almost every judge will issue temporary orders limiting the mother's contact with the child until the government can check out the allegations against the mother.
If your daughter has to wonder whether the paternal grandparents would try to take the child away from your daughter, I would say that the child should not be leaving your daughter. Grandparents do not have any right to a child against the wishes of a fit parent.
You would need to speak to a lawyer licensed to practice law in PA. Each state has completely different laws.
The information is for general information purposes only. Nothing stated above should be taken as legal advice for any individual case or situation.
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