I'm going to ignore and block my mother
Why do that to your mom?
Because she deserves it.
Ignoring your parents is wrong. You should not let your issues with them prevent you from getting close to them.
I don't know why I should be nice to her after she was so mean to my sister.
I don't know the entire situation, but you still should be nice to your mom even if she was rude to your sister. If you act unkind toward your mother, it will just further cause issues within the family. Instead, calmly talk to your mom and explain how you are feeling.