Saying "Cindy, you are wrong." or "Cindy, you do not speak for us." is one thing but, chanting "Cindy, Go Home." is telling her to 'shut-up' thus denying her her Freedom of Speech. Perhaps, chanting something about the successes of the War would be more Appropriate.
This is perhaps the oddest interpretation of the First Amendment I have ever seen. She was in no way prevented from exercising her free speech rights. Not being allowed to tell her to go home would however infringe on the right of those who wish her to leave.
I would also point out to you that the First Amendment is to protect us from government not from fellow citizens. There are civil penalties for physically preventing someone from doing something but the Amendment applies to the governments relationship to the citizen.