My niece.......(Vent)

OK, I need to vent about something. And I hope the necessary parties see this. I am venting on my blog because I actually cannot go to this person about it because it really is not my business. If I say something to the person it may cause more confusion than is needed. And honestly maybe saying it on my blog will cause the same amount of confusion, but it's my blog so I'll say what I want.

Children are a blessing. No matter their behavior, who their parents are, etc. If you enter a marriage with someone that has children, that says you are willing to be apart of that child's life. Here's what I am upset about. There is a child close to me that is being treated differently than her brother because she is the stepchild. Both parents (the father is biological) say that this is because her behavior is not up to par. But I know this child can feel the rejection from her stepmother, she may only be 7, but she knows when something isn't right. This of course angers me. The child is my niece. My brother's firstborn. He has a son with his wife and it seems to me the son is favored of my niece. Now both children are blessings and both children are loved. But my niece seems to be the outcast and I think she deserves just as much love and affection as my nephew. Now I know you're thinking, what could make you think that your brother doesn't love his daughter as much as his son? It's not him, it's his wife. For example, they recently bought a beautiful home. They have 4 bedrooms and a bonus room. There is a master, an office, a playroom, and a guest room. Now I believe my nephew sleeps in the room with his parents. When my niece is over she sleeps in the guest room. Here's my issue. They make this big to-do about this playroom for my nephew, but nothing in that house represents my niece. Is she not my brother's child? Recently my mother spent the day with my niece. While she was happy to have the time with her granddaughter, she felt as though they were just throwing her to the side so that it could just be the three of them. I don't think it's fair. I don't want my niece to grow up with the same rejection from her father and stepmother as I have.
Here's a thought I had. Though I never wish anyone to lose a child, I often wonder if my SIL had experienced a loss before having her first child, would she be softer toward my niece. Before losing Cameron, I never had much patience for children. After losing Cameron I felt I had all this mothering I needed to do, all this love to give but no one to physically share it with. So I'm a lot more patient with children. I love to hear a happy baby and want to console a crying baby. So I wonder, if she had ever been in my shoes, would she act differently. The life of a child is too precious to ignore.