>>>....I-90 to Chicago, then to St. Louis on I-55, and I-70 to Vail, Colorado.

Why be limitted just to interstates??

For example she could take Rte.61 N. from St. Louis to Hannibal Missouri (of Mark Twain / Tom Sawyer fame) then jump on Rte.36 West.... a straight shot to Denver that passes through a few one-horse towns that have "Twilight Zone" style cafes and diners, and extremely reasonable motels.

Time-warp experience of traveling old State Routes is tough to match...... Most are 65+ mph roads that pass through communities frozen in time.