TodoInTX, the rideshare board might easily work, but talking to your neighbors at the event might be even better. You can also maintain a flexible frame of mind. Maybe when she goes, you'll want to go with her. Frankly, I don't like everyone having to leave a party just 'cause I have to.
I cannot officially recommend it, because I'm not much of a hitch-hiker myself, but if it were just me trying to get out of the event and someone was bringing my stuff later, I'd go out to exodus with a big bottle of water, some sunscreen, electrolyte powder, a snack, a hat, sunglasses, 1 bag, and a sign marked RENO and look for cars/RVs from whom I got a comfortable vibe. A little to offer for gas is kind.
A huge number of vehicles are headed for Reno.