Why? Because it LACKS VISION.
If you are in a wheelchair, there is ABSOLUTELY NO REASON why you should be constrained to single-shot or even semi-auto NERF guns. What you do is, you go mount some full foam jacket on that chair and let Nana go to town. I recommend the Nerf N-Strike Elite Rhino-Fire Blaster (Amazon Exclusive); sure, it’s expensive. But, again, it’s your Nana. Don’t nickel-and-dime her fun.