How to be polite?

Jessica
My sister that is 34 I just turned 33 lives with me with her 3 year old daughter I want to ask her to move out. I can't deal with her parenting skills she used to be really good with her daughter now all they do is yell at each other. I get barely any sleep then work 6 days a week. My sister pays me between 50-100$ a month to stay with me. I pay all the bills. I know if I ask her to move out its going to create bad blood between us. I just can't deal with the stress anymore with my baby due in Dec I feel like my child will never get sleep due to all the yelling all the time. Am I a bad sister for wanting my sister to move out? She has been living with me since July 2012