At this point jusk ask her to move the water for your peace of mind. I’m worried this will breed resentment otherwise when her cat’s health fails, even if it’s only due to aging. If she respects you she will move the bowl, even if she believes it is totally unnecessary.

Indeed.

The next best thing: Talking buttons

If you want this to be successful, you would be wise to devote time to harness training (i.e. getting used to the harness) first. Don’t just put the harness on - it can be a bad experience for the cat and move you further from the goal of a walk.