Of course, the witnesses will tell this girl to expect opposition, even showing her Jesus' words about division in households.
It must be so hard for parents to just observe what is going on - but perhaps the best strategy is for them to research the organization. Yet, the last thing they should do is force their daughter to stop associating and tell her uninformed stuff about the organization.
I do not think what has happened is developmentally that strange: Around early adolescence, young ones are trying to "find" themselves and are drawn to idealistic belief systems - especially beliefs that echo some of the young one's anxieties about the "state" of the world. These beliefs can also be incredibly consoling in a big, scary world. The parents would do well to better understand the strong emotional appeal of religious beliefs for younger people.