Congratulations Monica! That's very exciting!
I'm also adopted myself, but I do consider my adoptive mother my "real" mother. When people ask me if I want to find my "real" mother, I tell them I already know who that is - it's the woman who raised me.
My birth mother, on the other hand, does not want contact with me. I don't take it personally, it's not ME that she doesn't want contact with, it's a point in her life that I represent that's too painful for her. She hasn't rejected ME, because she hasn't met ME. She's rejected what I represent.
I do regret that in order to respect her privacy, I cannot reach out to my two sisters who know nothing about me - my birthmom fears that her daughters will reject her if they find out. I never set out to disrupt her life when I searched for her. I am in contact and reunion with her brother (my uncle) and his family - including my five cousins and all of their children.
Enjoy your little sister! I'm so happy for you!