I totally know where you are coming from when it comes to feeling like your mother likes your sibling better. My mom is totally that way. She and my younger sister are very tight, and talk on the phone practically every night, even though my sister is 39. A few times my mom got really mad at my sister, so I was the "good" daughter for a little while, but it never lasts. It's just human nature I guess, and while I do take it personally, I know that I'm a daddy's girl, which is even better in my eyes. I have to argue all the time with my mother, and I never win in her eyes. I'm 42 and she accuses me of exaggerating details of a situation, totally making something up, or flat out lying. I know I'll never win, and it is really depressing to know that things will never change. I just have to hold on to the knowledge that I'm right, and my mother's inability to admit she is wrong is her problem. Heck, I hate to admit it, but I have three cats, and I do have a favorite. Luckily, the cats can't tell!!!
Please keep posting and let us know how you are doing.