quick question

My niece has been in my room around every 30min and poking the glass of my boa cage, the boa looks like it would strike but didn't. Is that angering the boa in any way?

It sounds like the boa is telling your niece to go away- and she does. The biggest concern I see is the conditioning that is going on. Your boa is being conditioned that he just needs to get into a strike/defensive posture and 'the thing wanting into his cage' will go away. I would be concerned that next time you go to take the boa out there could be problems. :(
My second concern would be that you are missing a terrific opportunity to teach your niece to respect the snake and the needs of the snake, and to teach her to read the boas body language; specifically the one that says "Go away please". ;)
Maybe you could arrange a time when the boa will come out of the cage and let your niece know that she will have the opportunity to hold it and touch it then, if she respects the needs of the snake now. :)

Sounds like a plan. I got the boa when she was a little over a year old and no-one wanted her 'cause she was mean but she's my baby. :)

Twitch, I don't know your niece's age but what has worked for me a lot of times is explaining to children that repeatedly tapping a snake's enclosure is like someone coming up to them and suddenly screaming in their ear. They get that simple equation very well (kids need to relate things to themselves and their experience to truly get it).

I would install a simple hook latch on your door so she cannot wander in there whenever she wants. It's very important for kids to be taught at an early age about limits especially as it relates to how they interact with other living things.

she's 12