How to help my mom with Alzheimer's remember she has to wear her boot for broken foot?

Can the doctor take the compliance out of her hands and cast it? Tough one, good luck to you.

Maybe try reverse psychology? Ask her to dig a 3-foot deep hole in the back yard. She'll ask, "How can I do that? I've got a broken foot!"
You say, "Oh, yes. I forgot."

Maybe don't remind her, but ask if her foot hurts, and ask if it feels better when she wears the boot. It ain't easy.

She has no care as she is in the stage that everyone steals from her and she won't trust anyone except me. She has this thing that if you remind her she will just go do it anyway and prove everyone wrong.

That's a very hard one. If only bribery and threats would work! I'm guessing that she has supervision overnight, but is alone during the day. Can you put masking tape over the velcro, along with a sign to tell her not to take it off? Can you put a big sign on the door to remind her not to garden?

If she can't remember, she won't remember. Sorry.