Congrats on being a first time snake owner! With snakes, patience is key. Also, remember that they are not like cats and dogs that crave our affection. I like to think of it as the snake tolerating me messing with them and handling them, rather than wanting it or enjoying it. To them, we are a big scary predator and they don't know if they should fear us. Build trust. It takes time, but is very rewarding.
BCI also don't feed as often or on very large prey, so be careful not to overfeed. I would recommend starting to hook train also so she knows feeding time vs any other time you interact with her. What I do with all of my boas is just reach in with the hook and lightly rub their head and body to let them know I'm there and that I'm not food. In time you will begin to understand her body language and know what she is trying to say with her posture and demeanor.
As far as reinforcing that hissing gets you to leave her alone, I don't really put that theory into action with boas. My goal is for the snake to have a positive handling experience. If a boa is being jumpy, hissy, defensive, or running away from me, I just leave them alone until the next time I want to handle. Every person is different and has different advice, so try a little bit of everything, and see what works best for you and your snake baby.