Kate,

I know she's only 3, but I'd try to explain it to her in a way she can understand, that mommy has a booboo that won't just vanish, one that has come to live with mommy for longer and that some booboos can't be kissed away, unfortunately AND that that's why you have to be careful around people with an injury or around people in a wheelchair! That's always a valuable lesson!

You know, just so she won't try to "help" you again... or anyone else for that matter. Slamming your foot down or more help like that is not something you want on a regular basis and she has shown and proven to you that she needs and deserves some kind of explanation. She clearly wants to help you and wants you to get better NOW. She just doesn't get it and that might become a problem. Right now she's powerless to help mommy, her help is all in vain, and she might not know how to deal with that at all without some kind of explanation. Talk to her!