Who is Erica Lane Lafferty from Under the Banner of Heaven: A Story of Violent Faith and what is their importance?

Erica Lane Lafferty is just 15 months old when she is murdered by her uncle. Although others had tried to talk Ron out of murdering the innocent baby he insisted she had to be killed also. First, she was listed on the removal revelation. Second, she was likely to grow up to be a strong and outspoken female, like her mother. Third, with her mother dead, the baby would be motherless so it would be better to kill the child also. As the men beat her mother, Erica calls for her mommy from her crib.