Old chicken help - aging or illness?

I have a Bluebell Hybrid hen. She is 4 years old and top hen. We love her very much. The life expectancy for a hybrid is apparently 4 years.

She went Into her usual molt over the winter and then started laying again in January. Since she's started laying again, the gaps have got bigger and bigger, to the point where she hasn't now laid in 10 days.

Bc she's not needing the food to make the egg, her appetite and activity levels have plummeted.

Today really worried me, she was sat very very puffed up compared to the other hens. She looked like a sphere. She looks depressed.

I've checked the following.

- she's been wormed recently.

- clear eyes, nares, no lesions in mouth

- small, shredddy poos bc she's not eating much

- normal white cap

- no abdominal fluid, acetes or EYP

-No palpable lumps or bumps

- comb and still tall and red, face red, skin good

-no mites

- weight fairly normal

-not laid in 10 days, but her last egg before that was good quality.

She still skitters over for her favorite treat (pine nuts) but she is less enthusiastic about any other food now.

I'm concerned she may be suffering with some sort of reproductive cancer.

Or is she just in her old lady years, and just not feeling enthusiastic about food and activity now she's not having to fluel that egg every day?

Do older chickens commonly just stop laying? Does anyone have experience in geriatric chickens? Do they go downhill when they stop laying?

I want her to be able to enjoy the retirement she deserves.

Thank you!