Well, it is not unusual for a hen in a hen only flock to crow. AND really there is nothing that you can do about it. Except to cull her if you don't like the eggs or the crowing.
This is really not a disorder that will be affected by feed. She might stop crowing if you add a rooster.
But...
It really is nothing to worry about. It is normal to have glitches in egg production. 3+ years, is getting on to be an old chicken in my world.
Good food, good housing, clean water and adequate feed-really that is all you can do, and accept the fact that nothing lives forever.