Here are some of what I picked out in the list (
http://www.child-abuse-effects.com/why-parents-target-a-specific-child-for-abuse.html). Some others could fit, but these are the ones that stick out with me and are JMO:
the parent abuses alcohol, drugs or other substances
post-partum depression -- 9 months postpartum and pregnant.
social isolation -- neighbors said they were not very sociable
poor coping skills - could feel overwhelmed with 5 kids and 2 more on the way
too passive -- Aliayah said to be shy
failure to attach (bond) with the child - in grandma's care most of her life
the child is viewed as an adversary (a mother might see her daughter as competition for her husband's attention; a father might see in his daughter a trait he dislikes in his wife and view her as an enemy) -- or maybe LL's mother's attention
the parent dislikes certain personality traits and quirks that the child exhibits, especially if these traits are seen as mimicking someone the parent is either suspicious of or has a particular aversion to (an estranged or abusive spouse, for example) - biodad maybe
the parent dislikes the fact that the child resembles in looks, someone the parent feels loathing toward (a spouse who has been unfaithful, for example) - again, biodad
the child was a product of infidelity, incest, sexual assault, or an otherwise unwanted pregnancy - not RL's child
child was born during period of extreme stress and crises - born while incarcerated
Then of course is the stepchild, which could be expanded to younger stepchild, female stepchild, biodad does not know about her so he's not involved with her, but other stepchild's dad is involved since he was on visitation.
Which is why I find psychology so interesting. I like to know why people do what they do.