Where are you staying the night before? We stayed at the Grand Canyon Caverns Inn which is only like 70 miles from the hilltop. More than enough for a LR I would imagine. We were from out of town so had a gas car so it didn't matter, but your answer depends on where you last charge is, and where the next one is after you hike out. If you can find something in that area around Grand Canyon Caverns Inn than you should be fine...but I'm sure it's slow charging.
The closest supercharger look like 119 miles away. Now that's pushing it (IMHO). I'd map out the elevation change between the two and make a decision.
BTW, you're gonna have a great time. Unbelievable out there.