Hey everyone - been lurking for a while on this one. So Sad
I haven't seen it mentioned, but this case oddly reminds me of the Skylar Neese case, where she was stabbed in the woods by her two best friends. The motive they gave was that they 'didn't want to be friends anymore' but also there was somewhat of a sexual relationship between the two killers. The reason I find the cases similar is because of the personalities of the Rachel and Shelia remind me of Natalie and David. Only one of each pair had a significant relationship to the victim (Shelia was a lifelong bff of Skylar and Rachel was new to the group). That person (Shelia and David) both seemed to enlist the help of someone who was a bit more malleable in the mind (Natalie and Rachael) and not as attached to the victim, but definitely looked up to/had a crush on the other killer(Shelia & David). Rachel also broke under pressure and confessed everything (like Natalie), while Shelia carried on like nothing happened and completely believed in her ability to get out of this (like David).
The reason I bring it up is because I think the motive of Natalie and that of David was different. David (Like Shelia) wanted to get rid of someone too attached to them, and Natalie (like Rachel) felt more of a thrill. Both pairs could have separated themselves from their victim without murder, and all were smart enough to do just that. I believe it was a combination of personalities that escalates "we should just kill her" being a thought, to an actual plan. If the mastermind (IMO) David and Shelia did not have a follower/pawn, I don't think either murder would have been followed through. Ironically, that's the person who got them caught.
It's also interesting to note that the both chose to plan, stab and leave in the woods over state lines. Social media also played a HUGE role in both cases and both young girls snuck out and never came home. That case took place in West Virginia.