One last possibility I feel the need to state, is that the grandparents attempt to do this old school and actually physically hold her until they can force her into it. Possibly in another country. It may sound far fetched, but its an unfortunate possibility that HAS seen fruition lately, especially if you're in Europe. Make sure that until this is resolved, she doesn't spend much (if any) time with them solo. If her parents support her in this, then time with the grandparents when they are present is fine. When they think they know what's best, adults will do stupid, shitty things to kids and teenagers. Do not let her put herself in a vulnerable position. If they do try it, regardless of whether they manage to hold onto her or not, IMMEDIATELY CALL THE POLICE. I cannot stress this hard enough, MAKE SURE LEGAL ACTION IS TAKEN. Almost anywhere you go in the western world, holding a minor and attempting to force them into legal contract, or extradite them to another country for said purpose, is not only illegal, its highly illegal. If they try it, its probably the only way to protect her for sure. After an attempt, she can't let them have any contact with her for at least a year for safety purposes. She should probably consider a restraining order of some sort too. Its harsh, but the risks are too high.