I'm not clear from the wording how long she was alleged to have been kept in the room. Evidently she was taken to the family party, someone seems to have been positive about that.
Did she say something to someone about them having hurt her? She might not have been believed, if EC and AJ denied it and accused her of lying. Early news reports state that Margaret was 'estranged' from her mother, to me that must have been the result of some kind of lies the couple told her mother.
I hope it will come out about how the fiction about Margaret was sustained in this small village and with family. Sometimes there are cases where the community is in denial, and don't want any 'troublemakers' to stir things up. Particularly if they have a strong prejudice against a person with mental disabilities.