Check her crop in the morning before she eats anything or drinks. That's the only reliable way to check that a crop is functioning as it should. The rest of the time, the crop will almost always have something in it, whether liquid or solid. Normally a crop has about a golf ball size lump as a chicken eats and drinks, and it won't ever stay the exact same all the time.
I’m so sorry. You did your best. It just wasn’t in the cards. She was fortunate to have a caring owner.