I do know of a woman just like this as you describe. She is the oldest of 10. I thought it was due to her controlling nature, but she does everything you describe in here. She has no filter of the mouth. She is very conflicting in her actions/words. She tells lies.
In this particular woman's case, she goes and cries to her grandparents constantly about her parents. She'll make up stories and slander her parents on Facebook. She has removed herself from her parents completely, but yet tells her grandparents that her parents don't want anything to do with her.
Her parents have kept their door open to her.
She also has been through several jobs, as she cannot get along with people in higher authority. She finally made a manager's position and is moved often because of her bad attitude.
To put the icing on the cake, while she is slandering her parents openly on FB to the world, she goes and digs out an old picture of herself with her parents. She gave it to her grandparents for a Christmas gift. It makes no sense.
She tells her grandparents that her parents don't spend time with her and all she wants is to go to dinner with them. But when invited, she doesn't show up. After hearing enough of the drama, her parents went to meet her at a restaurant she was working. She hid in the back and wouldn't come out. The next time they met up with her at the grandparent's house, they said they had gone to see her but she wasn't working that night. She replied that she was in the back and knew full well they were there.
It's an immaturity I can't explain. This person is only ruining a perfectly good relationship with her parents because she is jealous of the other siblings. It makes no sense. She is also almost 30.