She sounds like she's doing well for a chick in her condition! As for signs of malnutrition, you can usually fell how thin a hen is under her (what would you call it, keel bone? breast bone?). Thought this might not be very accurate until she's a little older. Growing chicks are as skinny as pencils.
You'll know malnutrition when you see it. She won't look well at all--poor feather condition, perhaps even leg problems, and just sitting around. It's your call. If you see her bouncing around and happily enjoying life without any pain, you could definitely keep her. She may need special care from time to time. It's up to you!
