How is it possible for a 42 year-old woman to have a multiple pregnancy?

It just happened to my mother's friend. She's married to her 2nd husband. She got pregnant for the 2nd time. She already has a 17 year-old daughter. She had C-section done recently; they were healthy quadruplets (3 boys and 1 girl).

She's already 42 years old. She had no fertility treatment done. There are less eggs at that age so having one egg fertilized is already hard. How was she able to give birth to 4 babies without any treatment done? Is that even likely or was it just pure, random luck?
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+1 y
She knows this runs in her family (though, the women were much younger than her) but she didn't imagine having 4 babies at that age.
How is it possible for a 42 year-old woman to have a multiple pregnancy?
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