Adding: It's true that you do weigh more. Due to your daughter's conditon, she may not be aware of the rough ride that may later cause sores or muscular aches.
How about a foam tire instead. The folks at airfree have been making them for years. Not sure about your area but most tire stores can order those for you and put them on.
http://www.airfreetires.com/Medical/Default.htm
Note: From personal experience on severa brands, I do not recommend air-free style tires for fast biking conditions esp on wet pavement. But I've heard they are save to wheelchairs etc.