Hi
Sorry to hear you are going through a rough patch, but as you say, lucky the motor cycle accident wasn't worse.
How old is Carl? If he is an adolescent, it may well be Marek's disease which is a very common and widespread Herpes types virus that often causes paralysis of a leg or wing although there are many other possible symptoms and your hen that died may also have been victim to it, especially if she was also adolescent. Sometimes it causes organ failure and they die suddenly, others appear to completely recover in a matter of a few days but often have a second and usually more serious attack months later. Some don't get any better or worse and some slowly waste away even though they eat well. The virus usually causes tumours and it probably would have been helpful to have had a necropsy done on your hen to establish a cause of death. It is worth considering that option for Carl if he takes a turn for the worse, especially if you have a large flock or are considering adding to it. I would definitely recommend you purchase chicks that have been vaccinated for Marek's if you decide to add to your flock in the future.
Unfortunately, there is no recognised treatment for it if it is Marek's, other than good nutrition and keeping the bird happy and stress free.
There are several very informative threads on Marek's Disease here on BYC, which I found very helpful is dealing with the outbreak I had.
Good luck to you and Carl and hopefully it is just strain and bruising injury to both of you.
Regards
Barbara