The Corid is safe for all ages. It is what is used in medicated chick starter...only stronger. I use a tablespoon per gallon... Little more won't hurt.
The sick hen, give plenty of water with vitamins and veggie or olive oil. Get some apple cider vinager and put some in her water also and make her drink it.... It will help change the ph level in her crop. I'd seperate her, keep her warm and not give her any chicken food. You can give very small amounts of safe food..I like parrot baby formula, but baby food...scrambled egg... But I'd get some poultry nutri drench vitamins..it absorbs quickly and help keep her body going until she can eat. This is a post that someone used Monostate to help cure theirs....never tried it yet myself. Important thing is to get that crop moving again... You can even inject the vitamin water mix under the skin to help absorbs ion since the crop is malfunctions..