Does laughing while seeking forgiveness count as mockery and apostasy that expels one from the fold of Islam, when a friend comments on someone, knowing that I do not wish to laugh but cannot control myself?

What is called commenting on people is often mockery and ridicule, which is a sign of ignorance, and it may constitute backbiting if the person being ridiculed is not present. Mockery does not reach the level of disbelief unless it pertains to something from the rituals of the religion. The listener does not share in the transgressor's sin unless he approves of it or is pleased with it, and laughing at it is a form of approval of the sin. Therefore, you must forbid your friend from doing that, and if she persists, you must leave her gathering, because sitting in a gathering of disobedience without condemning it makes the sitter a participant in the sin.