What do black birds eat?

What do Blackbirds eat? We took in what seemed to be an abandoned blackbird, that was very vulnerable and could not fly. Its mum and dad did not appear (till 2 days later- by wich time the bird was in the house.) She was not feathered at first, but now is. We have managed to feed it (a mixture of worms and soaked dog and cat biscuits (broken up), and it will now eat from the ground rather than expect its food to drop from above. I have put worms (in soil) in front of her and she has caught them. I do not yet know if she is able to sustain herself or know what to eat. Today she flew out of the garage by herself. Another fledgling flew nearby (fully feathered- a male perhaps her brither?) I have been recommended to release her (by a brid rehabber) away from the house so she does not know us. However as I say she flew out herself this morning. Can anyone recommend if she ill needs foods leaving for her or will she instincively know what to eat? What else might she eat in the wild?