What if, after running off from RD's house, she encounters someone locally who agrees to help hide her (for whatever reason, possibly sexually motivated). At some point over the next few days, Gaia's epilepsy escalates due to the stress and she dies. The person who's hiding her panics, because he isn't aware of her epilepsy and he knows she's a vulnerable missing teenager and possibly they've had sex or a fight, so there's some DNA evidence on her that shouldn't be. He worries he'll be done for murder.
A few days pass, and the person increasingly worries. It's too late to call the police. He decides to plant her clothes to make it look like a suicide attempt and that she's gone over the cliffs. He's stuck with her body or disposes of it further away.
It's very far-fetched but nothing makes sense!
