You have no idea how many stories I have read where an American goes to Hogwarts. Not only is this a very clique story but it is also an annoying Mary Sue. Please make your character a bit more realistic. As you are sure to know the age of magic begins at the age of 11... however before that children show their magical abilities.
This is not realistic and your OC is as Mary Sue as the other stories that I have read. Please try again later when you have a decent plot and a character that is more realistic then this one.