Let me be gentle it's psychological her psychology is not logical ,the best thing for you is to fly the nest make the best life you can ,and leave her to live with her decisions and attitudes .
Please also remember we have no choice of the family we are born into,but once thats done expanding your defintion of family does a lot ,especialy when your new family includes those that love you and care for you anyway anyday you are,get a good education , become all that you can be ,send her a mothers day card every year all other contact is really optional . I sound harsh but I went thru the whole toxic family thing , going back giving them chance after chance just to get kicked in the head again ,and to go thru therapy thinking it's me it's my flaw ,only to realise its not me, never has been,consider yourself ahead of the rest by knowing it's not you that has the issue , you will always have a sore spot kinda "ouchie" but it saves you from a big festering I hate everything spot. You've got this ,keep control, stay level headed and use going away to school as the catalyst to a great life , don't waste time on things beyond your control that should've been or could've been. Live your life for you ,they will be whatever they are , you dont have to be like them or around them.and when you graduate your real family will be with you ,that may include her or preclude her ,the definition of crazy is doing the same thing and expecting a different out come, your growing and changing maybe mom will to ,but don't try to manipulate life to get her to to change ,it will happen naturally if it's going to happen .