96 year old cannot walk. Anyone else have an idea how to get this through to her?

Your profile says that your mother has dementia. I know how frustrating it is to deal with repeated delusions, magical thinking, etc. but, I'd just try to keep in mind that there is nothing likely to convince her otherwise. So, I'd try to appease her for as long as possible.

Cajoling her may be the only way to keep her content. I used to say that things were in progress, doctor was going to be doing an evaluation, insurance needed some forms, etc. But, I did it with a smile and said it was good news. So, she was happy to have the good news. HOWEVER, if she really believes she can walk, I'd try to supervise her at all times, so she doesn't fall down and injure herself. Telling her to stay in bed or wheelchair, won't likely work, because she will likely forget what you said. Even if you say it every hour, she may have forgotten it in a few minutes, so, these comforts may need to be repeated very often.

I will say that eventually, she may likely progress from this stage and no longer ask about walking.

You might try writing up a short note on why she cannot walk anymore and either posting it on the bedroom wall or placing a copy on a bedside table. My mom has memory problems but still reads and this has helped with several things she needs to remember.

Your dealing with a person who cannot be reasoned with. She doesn't remember why she can't from day to day. Just fib a little. Tell her she can't walk until the doctor says its OK.