Lily Potter is a very smart woman, and she’s able to figure out that Voldemort is going to come to her house in a few hours, so she devises a plan to ensure that her husband and son will remain alive, this includes making a clone of James while hiding his real self in an abandoned muggle building, then when the clone is killed she is able to prepare herself to fight Voldemort head on, she barricades herself and Harry in his room and hides behind the door so that she can attack Voldemort when he least expects it, after she knocks him to the ground she takes his wand and snaps it, making him unable to hurt her or anyone else, then she uses her martial arts mastery to end his life, also because she used a muggle method of murder she cannot be arrested in the wizarding world, and because muffled don’t know Voldemort, she can’t be arrested in the muggle world either, she then retrieves James and makes sure that Sirius isn’t put into Azkaban by revealing that Peter was the secret keeper.