The SDLP councillor, who she says she was raped as a teenager by IRA man Martin Morris and that Sinn Fein and the IRA tried to cover it up, stood in silence among members of the republican party to highlight what she calls their hypocrisy over her abuse claims.
Sinn Fein politicians, including party leader Mary Lou McDonald and MEP Martina Anderson, led hundreds of marchers to commemorate the events of October 5, 1968 when violence broke out as police used batons and a water cannon to break up a banned civil rights march in Derry.
Ms Cahill said: “I wanted to remind them that they still haven’t managed to provide me with my basic human right of truth.
“(Sinn Fein) say they have no information about an IRA investigation into my abuse, which they absolutely do, and until they admit that they are still covering it up.
“They are calling for dignity, equality and human rights today which they haven’t afforded me.
“They can’t simultaneously demonstrate for civil rights while denying them to people that they don’t like.”