From Flagstaff you can now use 89T detour road which will take you into Page. Then continue north on 89 to Hwy 20 and over to I-15. We have not driven 89T yet but know of others who have and they said it a nicely paved road now. It used to be gravel before the landslide on 89. Now it's a well-used route to get to Page.
Newly completed US 89 bypass fully open with no restrictions
Or...89A to Jacob Lake to Fredonia and 390/59/9 to I-15 is also good for big RVs but your wife will have to close her eyes with the uphill approach to Jacob Lake.
We have taken the Fredonia route often with our 40'.