They don’t have to get a lawyer . From once she’s denying the child from doing medical or anything that has to do with the sponsorship , they need to outline this in a written document , send it to citizen and immigration, the only thing is ,in the future that child won’t be able to be sponsored by the father . I think there is a form to be filled out if the other parent does not want the child to be sponsored by the other parent . But you don’t need a lawyer.. just make sure they outline everything , what they tried, or how far they went and how they reach out to the other parent for this .