I think she was there because he was limited in time and option. I've heard a lot of people suggested that he wanted her to be found. Don't understand that thinking- especially with someone who has burned her head. Also, on a related note, some have also suggested the burning was out of remorse, or to erase what he did. I may have already said this, but that just can't be the case. Remorseful killers (often those who knew their victims) might place the body in a "comfortable" position, or put them face down or place something over the face out of respect and to shield them from the atrocity they just committed. Remorseful killers don't take a fire to the face of someone they just murdered. That act is perhaps even more brutal than the act of killing in itself. This person, in my belief, was not remorseful. He was evil and was covering his tracks with the only means he had available or could think of at the time.
If he wanted her found, he could have dumped her 5 feet off the road.
And I have never believed that she was taken away from BSR and returned when killed. This guy is NOT THAT DUMB. if we had someone who would bring a dead body back to the scene to dump it, we would know who he is by now. Way too much risk in returning to the area.
That being said, I suppose it's possible he tried to attack elsewhere on BSR, strangled her, threw her in the car, drove a short distance looking for the nearest spot to quickly get rid of her, noticed the path and put her in there.