I want to leave my abusive mother
How are you going to leave her?
I'm going to tell her that I'm leaving and then I'll disappear.
Separating yourself from an abusive parent is good for your health. A parent should take care of their child and comfort them, not abuse them.
I need to get away from her as soon as possible.
That's totally fine given her abuse of you. Your physical and mental health is most important.