I want to tell my teacher that she doesn't truly teach
Why do you want to criticize your teacher like this?
She teaches me things that I already know.
It is not a good idea to be so blunt when airing critical opinions with authority figures in your life. This will make you seem disrespectful.
It is not disrespect, it is an opinion.
It's your opinion, but it's also telling your teacher that she's failing in her job, simply because you are already a knowledgeable student. The rest of the class might not already know this information, so she is doing her job in teaching them. It sounds like you should be promoted to a more advanced class.