Is my friend's statement "All men are trash" subject to her bearing a sin on the Day of Resurrection from every man, and is what I deduced about the impermissibility of slandering a Muslim, and what Sheikh Al-Shinqiti mentioned, that a Muslim will contend on the Day of Resurrection with everyone who slandered him from a tribe or a country, correct?

A Muslim is advised to only associate with the righteous, for a person is upon the religion of his intimate friend. It is forbidden to insult a Muslim without right, and this is considered one of the major sins. Insulting a Muslim is a transgression (فسوق) and fighting him is disbelief (كفر). A believer is not a slanderer, nor a curser, nor obscene, nor vulgar. Allah has warned those who harm believing men and women without their having earned it, of slander and manifest sin. The Messenger of Allah, peace and blessings be upon him, considered speaking ill of a Muslim's honor without right to be among the worst forms of usury. Therefore, whoever insults men in general commits a great sin, and his dispute may be with everyone he has insulted.