Gangland thug John Lynch was sentenced to 13 years in jail last June for starting the blaze that led to her death.
Mari's dad, Richard Connolly, said he will spend a number of hours at her grave today with her older sisters, Lauren and Naomi, and her devastated mother, Teresa Keane.
"We will put a balloon at the grave -- it will be a very sad day," he told the Herald.
"I go up to the grave everyday, but tomorrow will be very special because it is Mari's birthday and all the family will be there.
"Lauren and Naomi are doing well -- they have been asking questions like, will Mari be getting birthday presents in Heaven?"
Richard managed to get Lauren and Naomi out on to a roof, but suffered serious back injuries when he fell backwards and landed on concrete steps, preventing him from getting the children down.
He managed to persuade Lauren and Naomi to jump on top of him, but Mari was too afraid and went back inside the house. She died in the early hours of October 3, 2011. Mari's mother Teresa was in hospital at the time of the fire, giving birth to twins.
Richard explained: "Yes, I will have this spinal injury for life. I still need a crutch and this will always be the case. But I don't mind about my injuries, I would just love to have Mari back."
When asked about John Lynch (34), the career criminal responsible for Mari's death, Richard said: "I never ever want to see that man again. I knew him to say hello to on the street before this happened -- but I would have never thought he would have been capable of what he did."
Lynch, of Church View, Boyle, Co Rosommon, is serving his sentence at Castlerea Prison for arson and manslaughter. The thug, who is originally from Sligo, has 17 previous convictions, including assault.