The planting of rubber trees is still a controversial topic in Africa, it destroys farmland and hunting land. One woman's story can be read here. Pro-planters claim the companies provide safe drinking water and education to the local populace.
Lynching is an extrajudicial punishment (usually a hanging), to intimidate and control a people. Violence in the American south against African-Americans rose in the aftermath of the Civil War. Unbelivably, mobs often took photographs of the lynchings and sold them as postcards. James Allen has published a collection and established a forum on Without Sanctuary: Lynching Photography in America (Warning: the images are graphic and disturbing).
Nettie is referring in her letter to female genital mutilation. Also called female circumcision, it involves the total or partial removal of the external female genitalia.