My mom wants me & my sister apart?

I don't know what to do. I am 20 years old and I have a little sister who is 12. My mom and sister are moving out of the state so all I want to do is spend as much time as I can with my sister. This past weekend I wanted to take my sister somewhere special so I told my mom I was going to take her to Laguna Beach, CA. (Live in Vegas 3 hr drive) and my mom went crazy, insulting me and telling me she does not want my sister to be like me, and in front of her! My mom said only this time, but she was not going to let her go out with me. Today I ask my sister that I would like to take her out to lunch for my break and she tells me that my mom called her and told her to tell me that she cant cuz she ate already,not true my sister loves being with me, I take her places where as my mom just keeps her inside the house watching tv. I never did ne thing wrong to mom it hurts when she tells me that cuz I do all I can, I work, pay her rent, pay bills, pay my school....etc. Talkin 2 her does not wrk