I think she's Akai's sister or somehow related to him, not only cos she has his eyes, but also from her background, she said she had lived in Americana three years ago, also Shuichi akai lived in America before, and I don't think she's Bourbon or nether an enemy, Conan said "That person's not an enemy, or somehow I feel like we've met somewhere before" and, "It mite be that person resembles someone I know, that's why the feeling we've met before is on my mind". And it could be that person is Akai.
Anyone who think Sera is FBI or CIA agent, don't you think it's too young for her age?
I don't know if she learnt of Conan true identity, but I think she's still suspecting him...