Comments on pufnstuf's timeline (my comments in blue):
3:01 PM - Mackenzie leaves the Academy of Hair Design where she works, gets in her car, and drives away. IIRC there was a news article that said the video camera time stamp was wrong, and the LE had made the correction to their timeline accordingly...do we have the correct time for this event?
3:40 PM - Mackenzie's phone data indicate that she is at/near the Riverfront Park boat ramp. While there, she sent a message to her boyfriend ("hey") and received a message from her boyfriend ("hey"). IIRC, LE said there was an incoming text, followed by an outgoing text. IMO and from my communications training, "incoming" means inbound to subject (MC), followed by outbound from subject (MC). Also, IMO it only means at least that her phone was there...not MC for sure. Anyone can echo back a text of "hey". IMO she could have already lost control of her safety at this point, or she was still OK.