Right, I think HH captured KG leaving at 1:49, so we don't know exactly what time she arrived, other than that the woman had to have arrived at the parking lot around 1:46/1:47, and reported no other cars were in the lot. Yet KG did report seeing a vehicle in that lot, which we now know likely had to be the woman's, who was the only other person in that lot. KG had to have pulled into that lot within only a minute or two of the woman, and KG couldn't have spent more than a minute or so dropping off the girls.
This is why I question the woman's "halfway" estimate, because I think the girls were likely closer behind her than that. If everybody walked a 10 min .55 mile, the woman could have gotten there around 1:58, saw the man on the bridge, turned around, walked only a minute or two, then saw the girls, who arrived at the bridge around 2, give or take a minute or two for all accounts. This would allow all the parties to be walking at a relatively normal pace and still give the girls time to take photos mid-bridge by 2:07 or before. In fact, this would give RA even less time to leave the area and BG to enter the scene, IMO.