My dsil (DH sister) is currently in labour with her first dc, a little girl!
I was telling my MIL that I was so excited to meet my new little niece and she scoffed and said "she's not your real niece, your not a blood relation".
I am as excited about this baby as I was my db's children and feel like I am getting a "real" niece. Now I feel hurt and like I am not a "real" part of the family 
AIBU to think she is my niece and treat her as I do all my other nieces? (I have no nephews!)