They may all eat the same feed but maybe she found a weed and munched on it and the others haven't tried it, another green yolk causer is usually infection, i wouldn't know how to fix that.
https://www.backyardchickens.com/a/common-egg-quality-problems
Can be caused by: - Feed or snacks containing cottonseed oil; - Ingestion of the weed Shepard's Purse.