I want to exclude my mother from my life
Are you serious? Why would you want to exclude her?
She is so needy. I want to be able to focus on my schooling.
It would be hurtful to her to be excluded completely from your life. Why don't you just chat about boundaries so you can have the time to focus on your needs as well as time to spend with her.
She is taking up too much time and I'm really busy.
I understand that you don't have much time for her, but you should always make at least a little time for your own mother.