Foster carer wants to take granddaughter abroad

Daughter lost custody of my granddaughter 16 months ago. A lot of lies were spoken in court by the father, who she kicked out when he became addicted to drugs and gave all their rent money to his mate in settlement of a drug debt. They were then kicked out of their flat and she told him she had had enough. The next partner she had unfortunately turned out to be controlling and physically and emotionally abusive and SS became involved because whilst daughter was in hospital he started hitting GD who told a teacher at school about it. SS decided to blame my daughter for the abuse and for not leaving the partner (she was too afraid to). She lives alone now after he kicked her out. SS basically guided the father as to what to say and do, told him to get married and his mother to buy him a house, which she did, then SS told the judge he had remarried and bought his own house. There is no way he could have done as he is still on drugs and has not had a job in 10 years. GD was placed with him, and three weeks later he and his wife had started hitting her. Again, she told a teacher at school who involved SS. The next thing we knew GD was living with her paternal grandmother. We have no idea where she is living, SS won't tell us and we have no idea what sort of care order she is under. The judge was not involved as far as we know so this arrangement was cooked up by SS and the paternal grandmother. SS have now threatened to withdraw daughter's contact, which is precious little anyway, if she doesn't agree to GD being taken abroad by the grandmother, who is foreign. We are desperately worried that she won't come back as her family are all over there. Does my daughter have to agree to this or does she have a right to object? Surely this is blackmail.
GD is five years old. Daughter is intending to take the case back to court shortly to challenge the court order.