She's a girl. This isn't cross dressing nor is it shounen ai.
Omg I'm so sorry I meant to reply to a different comment I'm sorry!!
Thank you for verifying this. I was five pages in and when she said that she's always been a girl I was a bit skeptical about the shounen ai tag. I was worried the manga would end up treating her like a boy anyway. I think I'm going to steal clear of this one.
*steer clear
The main character identifies as a girl. Sara is not a boy, she was just assigned male at birth. Please stop misgendering her and saying you'd prefer she "stay a boy". This shouldn't be listed as shounen ai. Sara is a girl :)