I can picture the author hunched over the script, going: "Wait, why did she ban her from movies? Crap, I can't think of anything."
Then their face just lights up. "I know!", they exclaim. "I'll make it a mysteryyyy!"
That's not what bothers me though. Well, it does bother me, but it does not make my blood boil. What does is that this lady seems to be thinking that she has to shield her fifteen-year-old, nearly adult daughter from the truth at all costs, so she spills it to a boy from her school who is the same age and can't possibly accomplish anything with this information. (Other than pass it on to her daughter, the one thing she specifically tells him not to do.) Either because boys don't experience trauma, or because he's not her kid so she doesn't care if he gets traumatized. And she insists on doing this even though her daughter already ran away from home because she can tell something's completely fucked.
You see, "the author wrote themselves into a corner and has to stall for time" is the charitable interpretation.
