Yes it sounds like she’s feeling jealous because she doesn’t want your MIL building a close relationship with “her grandchild”. She may have suggested you go earlier because she would expect you not to go but by making you feel hurt and rejected she could feel more special and important. When they get older though they do start getting frantic about not getting what they think they deserve (close family relationships). They look around at what other people have and think it’s not fair I want that too. Especially if other people have stepped up to fill the void as your MIL has. Be careful though because the appeal only lasts if it’s completely conditional, they want the fun parts of family to feel special and important, not the boring day to day grind that builds the normal safe bonds kids actually need.