The sheriff's have been very crafty to not generate any evidence of wrongdoing. Unless one of her direct reports decides to turn against her and testify there will be no evidence that she ever directly communicated the monetary requirements to get a permit. Prior to this it has largely been indirect evidence used to probe CCW issuance, looking at the correlation of donations to permits being issued and non-donors getting denied permits. Sheriffs have even quashed that in that many won't readily give out or accept the paperwork to apply for a permit so there is never a record of a denial that is subject to sunshine laws. If you keep it verbal, there is no evidence if no one will testify.

It simply may be that they don't have enough evidence in this instance to charge the sheriff.

Sadly you can't force anybody to resign for gross negligence, even if it was true.