The death by car theory posted here seems possible to me (have scrolled back and unable to find who posted it - sorry for not acknowledging.) She is sleepwalking, crosses road to get to beach, gets hit by kid returning home after driving illegally in the middle of the night, alone or with buddies. Even possible this could happen at slow speed as he is parking up (no noisy skid). He panics, hides the body to make it look like abduction. No obvious external injuries visible (eg maybe a crush injury). Gets round the issue of his having to extract her from bedroom without waking house etc. Might explain call for dashcam footage from Ardbeg. Doesn't explain how such an incident could happen so quietly in street, and not wake anyone. Police also implied her death was either at home or in forest.