He potentially might have offered to take her back to the club to meet her friends (assuming she told him where she had been and she had no key), a big ploy to get her in the car then he’s locked her in and she’s fallen asleep unaware of where she’s ended up I.e. at the park
Makes sense - I've lost count of the amount of times I've effectively passed out inside a taxi on the way home from a night of heavy drinking... It's quite scary when you think of it.
So he offers her a lift home/back to the club in a warm car, she drunkenly accepts, gets in, they drive off, she falls asleep, then he can take her to ORPFs without her even knowing and have his way with her.
<Modsnip - no evidence> Although we know PR was not discrete with his previous behaviours of servicing himself in public (on LS's road, oddly enough) and being a peeping tom, It seems unlikely he'd be able to persuade LS to go with him for that purpose in the little time they spent at the bench, in her drunken state, not to mention she would have been too drunk to consent legally.
(It's also remotely possible that they did go to ORPFs for the purpose of sex, but she then changed her mind to the dismay of PR leading to a struggle and her death.)
Only question this would leave is how could LS have gotten from the car park at the road entrance of ORPFs to the river bank? It's quite a distance, about 200 metres or so. If she thought PR was taking her home/back to The Welly, surely she would have been suspicious to wake up in a dark, wooded area? Maybe she was too drunk to think much of it but that seems unlikely; even when I've been straight up steaming I still have my wits about me.
Maybe he dragged/led her along and she tried to resist (would explain the screams) but she couldn't escape his grip.
Maybe to stop her screaming, he throttled her... and ended up killing her.
So he takes the body to the bushes or somewhere where it can't be found and flees in his car.
He cycles back later to move the body after looking on Google Maps for a good place to put it, and he takes it to the river and throws it in. He then cycles back the way he came; via Oak Road.