Many many thanks for the healing wishes; I appreciate them very much.

Below are instructions from the Department of Rehabilitation Services, The Ohio State University Medical Center; my best friend found their PDF, with diagrams (which are very helpful), and sent it to me. Might have been self-preservation on her part, since she was was one who had to help me dress when I left the hospital!

Putting on a Bra with One Hand
If you have an injury or stroke and are not able to use one hand, follow these steps to put on a bra. It is easiest to do this while sitting down.
1. Fasten the ends of the bra.
2. Pick up the bra in your strong hand with the straps at the top and put it over your head. Be sure the straps are at the top or the bra will end up being inside out.
3. Slide your strong hand inside the bra and push your arm up through the bra.
4. With your strong hand, pull the bra down over your weak arm. Lift your weak hand to pull it out of the bra. Your bra will be around your body near your waist.
5. Adjust the bra as needed with your strong hand so the cups are in front of your body and the straps are at the top.
6. Use your strong hand and lift your weak hand into the strap on the weak side.
7. Pull the strap up on that arm.
8. Put your stronger arm into the other strap and pull it up on that arm.
9. Adjust the bra and the straps as needed.
This worked for me. Too bad there weren't instructions for taking the thing off, too, as my usual methods did not work. I cannot, I learned, undo the bra I had on with one hand; just cannot do it, at least while it is still on.

So I had to try something else. I thought I'd pull one strap down (through my shirt sleeve) so I could pull my arm through it. That resulted eventually in my having one girl hanging out and the strap completely entangled with the sleeve, to the point of not being able to move either. So I moved the other side of the bra, which eventually had me bare-chested, still entangled on my dominant side, and wondering whether I was going to have to leave the house like that -- boobs swinging freely in the chill night air -- to find a neighbor to untangle me (and my shirt).

So I started gnawing on the shirt to try to free myself. Had I had the energy for it, there would have been cursing involved, but I didn't so there wasn't.

A brief vision of my half-naked body being found days from then flashed through my head. I gnawed harder, then started pulling at my shirt with my teeth in an attempt to break the tangle... didn't help. Pulled the front of the shirt up and over my head to free my head... didn't help. Pulled the shirt front and back over my head so it was all in front of me and tried to free the broken arm from the stranglehold... didn't help.

I put my head back through neck of shirt and turned my attention again to the sleeve-and-bra-strap knot. Straining my head backwards with the shirt cloth between my teeth and resisting the strong urge to damn the pain and grab something with my broken left arm (not that I could have), I managed to move one bit of tangle with my dominant hand, then a little more. Taking a fresh bite to take advantage of the newly-released fabric, I pulled back with my teeth again and clawed frantically at the knot with my good hand, gradually getting more and more of the tangle to come undone until there was enough room to allow me to free my arm of the shirt-and-bra-strap.

After that, it was relatively short work to get everything off me, finish untangling it, and put my shirt back on.

Next time -- should I ever leave the house again, I mean, while still in a cast -- I will not assume I can take off my bra without exposing myself (as I can normally) and will make sure to close the blinds before I attempt to free the boobies.