Have you told your niece that you want her to be a part of your wedding party? If so, have you considered asking your niece what she wants to be? The only reason I ask is because FI's niece is in our wedding party. She is 9 years old. I too thought she was too old for a flower girl so I was going to suggest she be a Jr BM. When we asked her to be a part of the wedding, her eyes instantly lit up and she said "Yay I get to be a flower girl!!!!". So there it was, we made her flower girl instead of Jr BM, LOL