FIRST TIME HEARING! My Chemical Romance - Helena | REACTION! 

Yes. It is about Gerard and Mikey's grandmother. She was very supportive of them forming the band and even bought them their first van to tour in. She became ill while the band was taking off and on a worldwide tour. When she died, Gerard felt guilty for missing the final year of her life and wrote this song from that anger. She was also a dancer and the girl dancing down the aisle is supposedly recreating a dance performed by Helen when she was young. I always looked at it as her dancing into the afterlife. Finally free of her burdens of age and Illness.