I will tell you what I tell everyone, live mealworms.
Go to petsmart, get a cup of live mealworms.
Put berries, melon, apple just something nice and nutritious in the cup of worms for them to eat.
Let the worms eat for an hour, take a few out for your chick and let her have them.
The reamaining worms, dump out their bedding and replace with chick starter so they'll eat and live off that you'll need to plop a berry or something in every couple days for moisture.
Offer the chick some grit to help process the goodies.
Guaranteed this method will strengthen that chick if it can be done.
Worms should be given twice a day at a rate of five or so.
Your other chicks would also LOVE them, but it gets expensive when you've got alot of little mouths.