I have been threatened with extreme violence if i go looking for my daughter in that country.I have tried to contact the school,but they refuse to communicate with me.Sorry, just read back. I would just try everything you can. Whatever negativity you get from Reunite. Also presumably the country your daughter is in does have a social services? And she must be at school. I think her school would report anything if they thought she was having a bad time at home. Could you also find out which school she is at and try to make contact via the school?
Otherwise the only thing I can think is to go there and ask for some kind of formal mediation with the grandmother.