I don't know if there's a TNR (trap, neuter, release) and/or foster organization in your area, but if so they can help get Mama spayed and the kittens fostered and fixed once they're weaned. If she's too scared of people to become a pet, she could go back to catching mice in your woodpile (and hopefully getting some food from you as well) without the stress of raising more kittens every year. Or she could get a job on a farm.
In West Los Angeles there's Kitty Bungalow And Charm School For Wayward Cats, their Instagram is adorable.