There are several possible reasons for a hen to stop laying eggs:

Age: As hens grow older, their egg production tends to slow down and eventually stop altogether.

Stress: Various factors can stress hens, such as excessive attention from roosters, aggressive behavior from other chickens, the presence of predators, or overcrowding in the coop.

Seasonal changes: During the winter months when there is less sunlight, hens may not receive enough light to stimulate the egg-laying process.

Inadequate diet: Hens require a balanced diet rich in protein and calcium to maintain optimal egg production. If their diet is lacking in these nutrients, supplementing their feed may be necessary.

It is also possible that your hen is still laying eggs but has chosen a different location to lay them. Hens sometimes have the tendency to hide their egg-laying spots, making it challenging to find the eggs. Additionally, other critters may find and consume the eggs before you have a chance to collect them.