She was between 4-6 years old when her sister passed. Yes it could definitely contribute to her anger and depression. She is doing the best she can under her circumstances. Don't judge until you walk her path.

Agree! I know it must be hard but she did not know her and well I think she has worse issues to work with like her anger that is still in need of work

I understand it is very hard subject and that it probably does hurt but did she even know her sister. Was she even old enough to remember her or her death. It sounds to me like maybe she is just looking for more attention.