Tonya,
I believe it is our obligation to keep the memory alive of those we love. Did you light a candle for her Dad? Or sit in a circle for 5 minutes and share stories of him with his daughter? It's important to help start some sort of ritual for your neice to remember her Dad. Afterall, if you teach her how to remember someone, she will know what to do when it is her turn to help others remember a loved one.
Also, remembering him will bring all of you a sense of comfort.
Eva