Rabbit Ears pass is 3,000' higher than Steamboat so not a big deal in 20 miles so 40 is a easy route. I would stay in the Grand Lake area and use the Yaris to go to Estes Park as a day trip. I thought E Park was a tourist trap 30 years ago. I usually stay in the USFS CGs south of Grand Lake and day trip into the park.
From Grand Lake I take 40 to I-70 and then Denver. South of Winter Park is Berthound Pass (11,300') which is a good climb but it's four lanes and by now you know to manually gear down and use your engine for braking on the way down.
Do you have a braking system on the Yaris? If not, then I would unhook it in Winter Park and let the DW drive it over Berthound assuming she knows to gear it down instead of using the brakes. Also at 10,000+ your non turbo engine is struggling for air.
If you decide to take the MH over Trail Ridge, then have the DW drive the Yaris.
