When the ovaries develop in utero, there are about 6 million eggs in them. By the time the baby is born, there are 1-2 million. Before puberty, a girl loses about 10,000 eggs per month. After puberty, her hormones have a protective effect and she only loses about 1,000 a month.

After puberty, only one egg matures and drops per month; the rest just resorb.

This explains it in more detail: https://www.healthline.com/health/womens-health/how-many-eggs-does-a-woman-have#eggs-lost-each-month