Our elders can be set in their ways but the truth is..... they don't like to be told from people who the think that they should know more from. When I want to get my mom or dad to do something.... I won't directly tell them.
I think you should speak to your vet on the side first and explain the situation. As him/her to tell your grandmother that she has to crate her. And that it is not a bad thing.... would she let a baby crawl around with out putting him in a pen? But have someone of authority tell her. You telling her is like 'waaa waaa waaaa' in her ears... it'll never work! Good Luck!