I'm glad to hear about improvements
Penelope is around 3yrs old? Is she starting to molt, do you know when she last laid an egg? With her age she may have something else going on and the respiratory illness could have weakened her and she is struggling. It's so hard to know - even though she is not eating well, see that the crop is emptying overnight, feel her abdomen for any swelling/bloat or feeling of fluid, also check her over for any mite/lice.
See if she will accept her feed made into a mash, chopped egg, tuna, meat, etc.
If she doesn't eat soon, you may need to try to syringe or tube feed her - you may find these helpful
http://www.backyardchickens.com/t/805728/go-team-tube-feeding
https://www.backyardchickens.com/th...d-pics-for-visuals-very-detailed-post.805615/