I got in a fight w/my mom, how do I show her Im sry? She was n th wrng bt im sry 4 mkn her feel like that!?

I didnt like the way my mom treated my lil sis (its been like this 4 several yrs now) I tried tlkin to her but it didnt work, I dont like to strt trouble but I just couldnt get up the nerve to tell my dad, I finally did but I had to get others involved to give me support or else I couldn't have done it! My mom and I were really close, now she wont talk to me or look at me, and when I come around she starts cryin, I feel like I did the right thing but why do I feel so bad! I luv my mom with all of my heart N it kills me to see her like this! I seriously thnk I m goin in to depression! Help Please! What should I do?