I think there is still some confusion as to where she was found. Hopefully it's OK to post this. Another user, Otto, posted this map (post #514 currently). The black #4 dot is where they found her today, right by the party area.
View attachment 361037
Thanks for clarifying that. That would seem the more likely spot for either her to drive into the reservoir on her own or for someone to drive/push the car into it.