I would not be surprised at all if the perp stalked her from Artmosphere.... and the truck was following her, on the phone with a second perp on foot to alert him when she drew near the ambush point.
They had both (or maybe even three) seen her riding by at times, and someone recognized her as someone who went to Artmosphere - ... they had seen her at BOTH places before.... both at Artmosphere, and also as she rode by the waylay point on her trips back home, and so laid an ambush for the next time they saw her at Artmosphere.
I'm so late to the ballgame, I'm sure, but I would guess the perp frequented the same places she went.... and either recognized her later on her night rides... or the reverse... saw her night rides, and recognized her at Artmosphere or wherever.
So my thinking is evolving on this.... I think that the perp(s) had seen her at BOTH locales, and so this was a plan, all the way.