As a Mother myself, I applaud your mom. Mostly because,
when our children get pets us parents usually end up the caretakers. I say that as a child who had pets and as a Mother. That's why I keep telling my 7yo no to a fish, because I know that her father and I will end up doing all the cleaning and water changes and probably the feedings too. I already have 2 birds, a bearded dragon who needs very very special care, a Russian Tortoise (he's really the 7yo's, but she still doesn't remember to feed him like she should
), a Boston Terrier and next week, we're adding a corn snake called Roseann Barr or RB for short (we've had corn snakes before), so I'm not interested in dealing with a fish tank!
Anyway, I have a GCC who's a little bipolar. GCC's are nippy, they often have Napoleon Complexes, they can be bullies with other birds, they can give you real attitude and mine can sometimes be downright mean. That said, they can learn to talk (it's up to each individual bird and smaller birds do seem to have a harder time, so don't get one thinking it
will talk), they are real snuggle bugs, clowns, inquisitive and just downright awesome. One of the members here has a GCC who plays fetch. It's seriously too cute!
I don't find my GCC to be messy. I mean, you have to clean their cages; change papers/liners every other day at minimum, do a good wipe down once a week. Fresh food and water daily (and by fresh food I mean actual fresh fruits and veggies, at minimum, not just pellets but those should also be fresh, as in don't give them a full bowl and let it sit for three or four days getting stale). Be prepared for some screaming. The Conure scream/screech is high pitched and sort of ear piercing. Some scream more than others (mine rarely screams) and they will call out and chirp and making lots of noises throughout the day. Again, some more than others. A GCC is typically quieter than a Sun.
My GCC also has food and cage aggression, so that's something to keep in mind. My Goffin's Cockatoo does not, but all birds can be prone to the cage aggression. My Vet said the food aggression is unusual. They also require attention. How much time are you going to have between school, after school activities, homework, a part-time job, a boyfriend/girlfriend, etc? You are in High School. In High School, I didn't have enough time for a pet because of the after school activities I participated in and my job. I had to pass up a dog of my own because I simply didn't have enough time for one and I certainly can't imagine trying to own a bird at that time.
However, if one really wants something they will commit to it to the fullest of their ability. So if you think that you can provide the care and the amount of time a GCC will need, all the more to you. They are also very social animals, so if your mom is willing, she could also help in the
attention part, and maybe even allow the bird a place in the highest traffic area of the home so it can get interaction throughout the day?
I wish you luck and give you and your Mom extreme kudos for doing research before buying.
and of course you can always lurk around here when bored to learn all about the little terrors we love so much. 
