Can I be really blunt -- as someone who sews a lot of things for people with disabilities *and* sees how the use patterns go in real time? Skip all the features, unless they are specifically requested by the person you're making this for. A pocket that doesn't sit just where it should is a pain in the butt and annoying. Straps may or may not have anything to strap to, depending on the specific chair, and even if they do happen to fit, they are a liability for transfers. Velcro anything invariably snags things you don't want snagged, or irritates fragile skin, not to mention picking up lint in the wash. Anything that requires explanation will be an annoyance to the staff or helper.
Just make her a lovely lap quilt small enough that it won't catch or drag. If she doesn't use it as a lap quilt, it could look nice as a bed runner or a table topper or over the back of a couch. Alternatively, it would be super for a lap quilt in the car or at a medical visit. By making something that is just basic and lovely, you have far greater chances of it being loved and appreciated.