D.K.
We just strapped my son in. It was in no way punitive, we just put him in his chair and locked it at the start of the meal. Soooo much easier to avoid this battle than to fight it. If she does stand up, then try telling her (politely as you have been) to sit down, then if she does not, repeating it, while helping her to sit down. If you just keep talking at her instead of physically assisting her to cooperate, it's just a game.