Shaping behavior

How do we as humans change the way we behave? Some studies suggest that through operant and observational conditioning we are able to reshape ourselves to behave in a way that we would like. Take for instance my four year old cousin Ranyia she needs to learn how to act more like a child and less like an adult.
Ranyia is constantly around adults while she is out of school. She mimics her behavior on what she sees and hears her mother and other adults say. Thus for, making her behavior that of a tiny adult. She was an only child until her mother gave birth to her younger sister which has made her behavior far worse than what it initially was.
With Ranyia I tried to use coloring books and crayons but that seemed to work only for a couple of minutes before she was right back to being in adult conversations. I also tried placing her in time out because I can’t bring myself to whoop a child that isn’t mine. The more I ignore her behavior the more she becomes intolerable.
For my first experiment I told her that if I had to say something to her about her behavior that I wouldn’t take her to the movies. As I watched her throughout the day she behaved like a regular child. All she kept repeating was that she was going to the movies or more so hanging out with me. The next day and days after that leading up until Friday her behavior was alright. When Friday came around she complete did a 180 and went back to acting out and being unruly. So I told her that we weren’t going to the movies and that she would have to try again next week. This resulted in her running to her mother crying about why she couldn’t go to the movies and that she wanted to go now. I pulled her over to the side and explained to her that because she decided to act up we weren’t going and that only good girls go to the movies.
The next day I woke up and she had packed my shoes in a bag and told me I didn’t stay there. She also stated that she would get my brother to take her to the pool because she didn’t get to go to the movies. I didn’t get mad or angry I sat her down again and explained that she wasn’t going anywhere and that she would stay in the room until her mother was ready to leave. She didn’t listen and ran around the house. I didn’t say anything the whole day to her. When she walked up to me asking for a hug I ignored her and pretended I didn’t even she her or hear her talking. I went back to my apartment for a couple of days and her mom was calling me for here wondering when I was coming back over. I explained that she acts up when im there so maybe when she doesn’t her me her behavior will change.
The next time I talked to her mother was a few days later she had told me that Ranyia wakes up everyday and calls her self cleaning up in hopes that I will come back. That’s when I knew that she wanted attention because the new baby was taking up her mother’s time. I realized that it also meant she needed to socialize with kids her own age.
I arranged for my brother and his girlfriend to pick her up and take her out to the local pool. Therefore she gets away from being around her mother when she has her attention on the baby and not on her. Also she can meet kids her own age and interact with them on her level. She also got rewarded for trying to clean up and act more like a child than an adult. To maintain her behavior I let her know that every time that she acted up that I would not come around and see her. That she wasn’t allowed to go anywhere unless it was with her mother. Soon after that she has been going to the pool and the movies because she wants the attention she was getting at first before the baby arrived.