I don't think you need to cut out Paris entirely, just look at other options for getting around the city instead of walking or taking the Metro which requires a lot of walking, stairs and energy. Focus on confining your sightseeing to small pockets/specific neighborhoods each day to not spread yourselves too thin. And stay as central as you can afford to so you are able to come back to your hotel or apartment and she can rest as needed. Wherever you stay, make sure it has an elevator.
Examples to get around Paris easier would be the Hop On/Hop Off Bus (although there are ways to do similar via public transit routes like Bus #69, but no guarantee you are going to get a seat if the bus is crowded), or you could splurge a little and book one of the Citroen 2CV private car tours and see the city in a convertible. Get the Uber app on your phone and use that liberally. Take one of the boat tours on the Seine, especially as it gets close to sunset. Instead of standing in the endless security lines to get into the Eiffel Tower and go up to the top, enjoy it from the ground and have a picnic dinner. Or go somewhere else that has a nice view of it - check out the view from the Montparnasse Tower instead which has far fewer crowds and a quicker elevator to the observation deck level. Go see one of the free fashion shows in Paris at the major department stores and while you are there, go get the elevator/escalator up to the rooftop terrace to take in a 360 degree view of the city. Or take the elevator up to the top of the Arc de Triomphe (also open late and less crowded) to get a nice view from the top.
If she likes museums, maybe focus on just a few of the smaller ones like the Rodin or Marmottan. Or take advantage of the nights when some of the larger ones are open late and go a few hours before closing to see a few select areas. Maybe they have a wheelchair on-site that you can use to cut down on the walking around in some of the really large places like the Louvre.
If anything, Paris is a great city for people-watching. There are so many cafes where you can just sit at a table outside and watch the world go by and relax. Same with the number of parks and gardens scattered throughout the city.
Outside of Paris, I'd look at maybe spending some time at the beaches in the south of France where you can just rent some chaise lounges and relax. Or head to Provence, rent a car and you can stop at the places that interest you and travel at a very relaxed pace. If you want to stick to Northern France, maybe rent a car and travel around Normandy instead.
Work on scheduling the activities for times of the day when she has the most energy. For example, if she does better when she first wakes up, then spend a few hours in the morning sightseeing, stop well before she starts showing signs of fatigue and have a long lunch somewhere. If after sitting for a few hours eating lunch she still has some energy, then move on to some other activity, if not, just stop for the day. There are no rules that you need to see a certain number of tourist sites each day to make your time in Paris worthwhile, and it's perfectly ok to not see any at all if your daughter is feeling a bit worn out.