Sorry about your rescue bird.
The more snacks you feed your chicken, the less room there is in its tummy for its well-balanced commercial feed, which supplies all the nutrients it needs. I agree with @Wyorp Rock, an all-flock formula is very good for all your birds, especially if you have some that are not laying, like males, young or old birds, or some who are molting. Only birds that are actively laying need a layer formula; it contains too much calcium for everyone else and can be hard on their kidneys. Keep some oyster shell in a separate dish and only the layers will help themselves to as much as they need.
The more snacks you feed your chicken, the less room there is in its tummy for its well-balanced commercial feed, which supplies all the nutrients it needs. I agree with @Wyorp Rock, an all-flock formula is very good for all your birds, especially if you have some that are not laying, like males, young or old birds, or some who are molting. Only birds that are actively laying need a layer formula; it contains too much calcium for everyone else and can be hard on their kidneys. Keep some oyster shell in a separate dish and only the layers will help themselves to as much as they need.