How do i deal with a bratty niece?

She is a spoiled brat...her parents aren't going to change because you think they should or tell them to, so I would just leave that alone. However, if you are babysitting her or just playing with her when your sister visits or you visit them, then simply tell her you will not do as she demands and if she would like you to play with her then she must behave. If she doesn't listen, don't play with her and certainly don't do as she demands. If she runs crying to mommy so be it...doesn't mean you have to do as your sister says...if your sister wants you to babysit or play with her child then tell her that her child needs to respect your authority and listen to you and if she doesn't then you will not look after her or play with her. You must lay down the law on your part if you want to be able to enjoy time with your neice a;nd who knows...if your sister sees that her daughter behaves for you and not her, then she may start standing up to the plate as a parent instead of being a pushover and letting her child run the house.