I can't tell from your post why it is she feels you need to continue twice a week and why you want to change to once a week. Sometimes in a difficult place in therapy we are tempted to quit; the exact opposite of what we need and the time to hang in there!
I would suggest you trust her and follow her treatment plan, which includes twice weekly sessions for now.. It is your decision, yet you have asked for her help and she feels twice weekly visits are what will help you.
You might feel she isn'l listening to you or understanding you and you may need to talk more about it; it's important to you. Stopping therapy because of this disagreement won't help you; it would be retaliation. Keep going and keep talking to her about it so you can both understand each other.
If she is concerned for you, it may be her ethical responsibility to advise your parents.
ECHOES