H.W.
S.,
My heart goes out to your niece. I lost my dad when I was 14 and I was the one that knew what my father wanted for arrangements, where his important paperwork was - everything. My dad was my rock & my world just stopped - even after 23 years, it still bothers me.
I was kind of spoiled by my dad - I was Daddy's Little Girl & I was the youngest (out of 6). After my dad died, I had to go live w/my mom. She had to ween me from the spoilings of my dad. But, she never arranged an appointment with a counselor for me. As I look back on it, the counseling would have done more good for me then, than letting me 'deal w/it' in my own way.
Each member of the family has had a different relationship w/the decedent. The relationship, as I'm sure you know, is special between a parent & child. Your niece is need of someone outside of the family to talk w/to get her feelings out. This may take her some time, but that weight on her shoulders must be pretty heavy by now.
My advice to you, is to have a serious, sit-down discussion w/your sister about getting her daughter into counseling w/a child psychologist. And because its been 3 months since her dad died, and the new baby, the sooner your niece is active in counseling, the better your niece will be.