She ended up choosing the Chicco Keyfit 30 travel system. The choice was based on having the most features that could be used with one hand, and the ability to rest the carseat on the wheelchair armrest (with support). This is not a light carseat, and with me in it, it's darn heavy. But mommy can use all the features (not easy, but possible).
It seemed that lengthening the straps would require two hands. That is, until mommy figured out she can push that front orange button with her thumb, and reach underneath with the rest of her hand to pull the straps from the bottom. Here's a video to illustrate:
Here are some photos of mommy getting me out of our van in my carseat from the base onto the wheelchair armrest:
Here is the stroller that came with the travel system. It works great, but it's really big!
Mommy found this one which my carseat snaps right into and it's much more compact!
Notice how the handle is one piece instead of two. Here we are in the stroller:
(Mommy is very serious about shopping at Target)
Here is how mommy pushes my stroller from her chair.
All in all, we are very happy with this system (Of course, it's the only one we've used). Happy Travels!