My sister has 5 children. 4 girls and 1 boy. For the most part they all love each other. My sister is really crafty with money and making a dollar last. She struggles with things but is very strong minded and has the will to make anything happen. EXCEPT trust her oldest daughter. My niece started rebelling at age 14. Sneaking make up, shaving her legs, plucking eyebrows, etc... All done without consulting her mother. So, my sister thinks she did it sneakily. Well, since those early issues my niece has been caught lying, getting in trouble at school, ditching school and even had a secret romance once or twice. The nieces that are close to 16 years old are both quite the opposite. 1 is disabled and the other is a straight A+ student, would rather stay home and loves to cook. She does chores and is almost perfect. My sister embarrasses her 16 year old by telling people (mostly family) what terrible thing her daughter has done, now! I know neither of them is perfect, but geese I love them both and I dream of the two of them getting along again. I think my niece is so doomed to do everything wrong and my sister is not easy to talk to. What can I say or do to remind them of how they used to love each other so much. Is it possible for my sister to begin to trust her daughter again? Can my niece put her teenage life on hold long enough to earn my sister's trust again? Who gives first? My sister is starting to resent my for even sticking up for my niece. :confused:

Apparently there never really was good communication between the two of them, or something broke it. The teenager has to be willing to cooperate so her mom can trust her and her mom needs to communicate more with her. If the mom is embarrassing her daughter in public, then that's not showing any support and therefore agravates the teen's need for outer attention. I think you're the link that they need in between, but you need to show support for what's right. Not only for one side or the other. Maybe you can help boost up the teens self-esteem if she needs it, by making her feel that her mom loves all her kids the same and that so do you. One thing that you must never do is to make any comparison between siblings, and to never crush their sense of self by doing those things like embarrassing them.
You know perhaps it will pass by with time, but they both got to put their input into the situation to make it better. I hope this helps at least a little.

You might be able to mediate, but only if you approach it right.
Try starting a conversation with your sister highlighting your niece's achievements. If she gets annoyed, just simply say. "Look, she's a good kid trying to make a good impression on you. Take a second to recognize the good she's done." And leave it at that.

Don't come between them, it'll will cause problems later on. Just be a friend to your niece and try to wait it out. They'll come together when they're ready.

Thank you for your advice. I will give it a ttry. I'm really tfrying not to pry but at the se time I am leaving them both with something to think about as I just be the good listener. If I think one of them is out of line I think I have th right to say something. But on a diffedrent note, I too have a pre teen and I am also learning as I go.