I agree with you that the road from Moab to Monticello to Cortez is a great two lane road for US---most of our city fellow riders might now agree---hehehehe
If she is really adventuresome, you can take the La Sal cutoff road through Naturita over toward Montrose and once on the Western Slope---she would see Silverton and the Million Dollar Highway---which I agree is rather breathtaking but in July should be heaven----as long as she is driving a good vehicle. But as you point out, if she is coming from the almost any direction, the fastest route really is across Utah on I 70 to Grand Junction and then down the Western Slope.