Has she laid eggs since you got her? What do her poops look like, and pictures are welcome. Is her crop empty or full first thing in the morning before she eats and drinks? Are the others letting eat the food? Getting a fecal float on some of her fresh droppings would be ideal if you have a vet...
You can use Tums, but it lacks the vitamin D 3. I would break Tums in half and give her enough for 300-600mg orally. Just open her beak and place it inside. Yogurt has some vitamin D, and plain is best. Sardines, salmon, tuna, egg yolk are some other good sources.
They can have a bit of diarrhea, and it tends to get into the feathers and build up. If you can bring her inside to soak her butt in warm soapy water, then dry her off and blow her dry, I would. Offer some cottage cheese, about a TB full and some probiotics may help. If she has not been wormed...
You only would add a drop or two of the peroxide into the ear canal, and then clean it out. Then use some Neosporin ointment inside. The Neosporin can also be used into the eye twice a day to treat infection in the eyes. I would bring her inside once a day to treat, and then put her back out. Or...
If you have mosquitoes out and it is warm weather, fowl pox might be the cause. That is a virus that lasts about 3 weeks and clears up without treatment most of the time. Here is a link with pictures of how pox can look:
https://the-chicken-chick.com/fowl-pox-prevention-treatmen/
After the coconut oil, continue to massage the crop a few times today. Offer some fluids. I would also let her out with her flock so she doesn’t get picked on when she goes back after too long a time.
I am not a vet, but due to the symptoms and the enlarged liver at 16 weeks, I would wonder if avian lymphoid leukosis might be the cause of death. Sorry for your loss. Here is some reading:
https://www.slideshare.net/slideshow/avian-leucosis/82389838...
I would try to get all of the pus out tomorrow. You can apply a couple of drops of hydrogen peroxide into the ear canal. Then clean it out with QTips gently and apply some plain Neosporin triple antibiotic ointment daily.
You give the miconazole directly into the beak.
Crops should only be massaged if they are firm. If they are squishy, massaging the crop can push liquid back up into the throat, causing choking. I would offer her a little bit of chicken feed mixed with a lot of water to eat after you check her...
I would let her back with others to increase her appetite. The yellow urates can be a sign of liver problems or sometimes dehydration. That may be due to a reproductive disorder, and MG can sometimes be an issue with that. Offering the chicken feed made wet with water in a small bowl is a good...
It could have pus inside. If you clean it with disinfectant and do lance it with a sterilized needle, just don’t get it into her eye. Have someone help you hold her wrapped into a towel if you decide to drain it.