Is it permissible to beat, torture, or kill a person who assaulted a girl in her childhood, causing her to lose her virginity, this being after the girl's marriage?

The girl made a mistake by telling her. Both of you must repent from the relationship before marriage. You have no right to harm anyone, even if their guilt is proven; it is the ولي الأمر (ruler/authority) who implements the حد (prescribed punishment). Islamic law has strictly prohibited aggression against a Muslim without right, and has emphasized this. Allah Almighty says: "And whoever kills a believer intentionally, his recompense is Hell, wherein he will abide eternally, and Allah has become angry with him and has cursed him and has prepared for him a great punishment." (An-Nisa: 93). The Prophet, peace and blessings be upon him, said: "A believer remains within the scope of his religion as long as he does not shed unlawful blood," and "Indeed, your blood and your wealth are sacred to you." The bankrupt person is he who comes on the Day of Resurrection with good deeds but has aggressed against others. His good deeds will be taken and given to the wronged, and if his good deeds are exhausted, some of their sins will be taken and cast upon him, and then he will be cast into the Fire.