When we got our two cats (they were buddies in the shelter, so they came in a bundle) one was super scared of everything. The first two weeks we only noticed his presence in the middle of the night, when he came out of hiding to eat. Then he started drinking out of my water cup, which is on my desk next to me. A year later I'm drinking out of a bottle and he has still his favorite cup on my desk :) the other one is using a fountain.

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.