Maybe she is passing air. I would stop giving oatmeal. She should only be given chick starter at her age. Does she have any puffy spot of air under her skin any where on her body?
Sorry for your loss. Yes, that is the Corid you want and it is also for chickens. Dosage is 2 tsp (10 ml) into each gallon of water given as the only water source for 5-7 days. You may also give some undiluted Corid orally 0.1 ml per pound of weight as a boost or jumpstart once or twice a day...
There are a number of good articles including this one:
https://modernpoultry.media/internal-parasites-in-free-range-chicken-farming-roundworms/?mp=1765813874375
https://birdvetmelbourne.com/worms-in-chickens/
https://farmanimal.elanco.com/au/insights-centre/understanding-worms-in-poultry
Virkon-S tablets added to water and used in a spray bottle or garden sprayer is available from Amazon and is a very good disinfectant used in farms and around chicken coops. Are they still sneezing regularly? That could be a virus called infectious bronchitis, and there is no treatment for...
I would probably use the expired Tylan 200 orally as long as it was kept clean. Dosage is 0.1 ml 3-4 times a day. If she starts drinking well the Tylosin in the water would be good.
Here is some reading about lash eggs and salpingitis:
https://the-chicken-chick.com/salpingitis-lash-eggs-in-backyard/
https://poultrydvm.com/condition/salpingitis
Dawg53 is a good source on worms and tapeworms. Since tapeworms can be reintroduced by the chickens getting the worm eggs from droppings of a chicken with tapeworms, and by eating insects, beetles, worms, and mice that are intermediate hosts of tapeworms. Keep droppings picked up as possible...
Was the shell or have the recent shells been soft or thin? If not, and since she passed the shell, I probably would not. But if they were, it would not hurt.
Do you have any pictures of the lash egg? Lash eggs are a product of salpingitis or inflammation of the oviduct. Here is some reading about it:
https://the-chicken-chick.com/salpingitis-lash-eggs-in-backyard/
https://www.bhwt.org.uk/hen-health/health-problems/lash-eggs-salpingitis/