Daughter is insistent about getting a sister

So before I got pregnant with #2 I floated the idea that my toddler could have a little brother or sister... And right away she said "no brother, only sister!" 😂 I tried telling her we can't control that but it doesn't seem to have gotten through. Since then we're 12 weeks pregnant and finally told her the news, and again she said "sister!" And will now only refer to the baby as her sister.

We want to keep the gender a surprise so I'm a bit worried how she'd take the news if it's a boy...in the end some of her best friends are boys so I think she'd accept it eventually but she sure has her kind made up right now! It's a bit funny how sure she is!