When PR encountered Libby at the Endsleigh entrance, she was not far from home and heading in the right direction for her road. He was very local and very familiar with the local area, but he does not mention asking her where she lives until after she is in his car (doors locked?) yet he does suggest that he give her a lift home. In the car, he says that he asks if she knows where she lives and she says she will show him.
My point is, that if she could show him at all, it was so close that it might have been possible to begin with, if they had walked there, and he could have supported her to get there - but he neither asked her where she lived nor suggest that, because he wasn't going there anyway, he took her to his car instead.
But she was not in a state to show anyone how to get her home once in a car which then drove in almost a circle and did a few turns here and there before stopping at oak road, a much greater distance from her home.
PR, whose first language is not English and who has needed a translator throughout his dealings with the (sober) police, has been able to report every word she said to him, clearly and with confidence, yet other people who have not needed translators have reported that they could not understand much of what she was saying because her speech was so slurred and indistinct, and it even seems that Libby became frustrated with them for this reason. PR did not need to know what she was saying.
Also: from his own various reports of what happened in a very short journey in his car (5mins?) PR has reported that she tried to undo his trousers, scratched his face and took of her own knickers all whilst directing him to her home, he did not stop the car until he arrived at a very secluded and lonely place which he also knew very well.
That's why I don't think he was trying to help her.