At MK, Epcot and AK the strollers are a plastic, low riding stoller. The seat back is upright, but there is plenty of floor space for her to strutch her legs in. They do not recline. The do have a large canopy so unless she is directly facing the sun, it is shaded. There are several large pockets in the back for storage. At MGM the strollers are like the jogging strollers. They are made of a mesh material and lean back slightly more than the others, though they don't recline. The MGM strollers also sit more like an umbrella stroller as far as the leg position goes. They also have a canopy and pockets, though the pockets don't have as much room as the others.
When I took my sister last year (5) we rented a stroller every day and she never complained that they were uncomfortable. In fact, I think she rahter liked the plastic ones. We didn't take our own because I find the handles on her umbrella stroller to be too low and thus uncomfortable for me to push, not to mention that I always kick the wheels with my long strides.
Hope this helps. Not being the mom, I can't make any suggestions on types of stollers if you decide to take your own.
Tia
162 days til our return to the Movies