I cant stand my 7 year old niece

My sister has 3 kids 2 girls 1 boy . I have 2 toddler boys and a little girl on the way. My brother has 1 son. My sister 7 year old daughter is horrible and i mean horrible. She doesn't listen at all. She will get smart and tell me what shes doing and i cant do anything about it. I never get a break from my kids my sister has 2 in school ( her 12 and 7 year olds) she has a 20 month old at home only during school days and my mom has the 7 year old every single weekend or any day shes off school. Today i went to do laundry and spent time with my mom with my oldest. As soon as i went to pick my youngest up from his dad my sister called and asked what i was doing. I told her picking him up going back to moms. She called my mom and told her she was dropping the 7 year old off. She knows neither my oldest or 7yo listens when together. She said oh well. She then called me to pick her up. I told her the same thing they wont listen. She didn't care. I told her ill just pick my son back up and leave. She said thats fine but 7yo was going either way. I picked her up and took her. She begged to play with my son i told her this was it and she better listen. She didnt. I had a appointment for a tux fitting for my oldest for sister wedding and of course 7yo demanded to go and wouldn't listen when told no. She literally ran to my car and got in and wouldn't get out. I told her she goes she will be going home. My mom said the same. She went and screamed the whole 15 minute drive. I had to blast my radio to try and drown her out she yelled over it. We get there and she refuses to go in. I had to fight her in to the store while pregnant (high risk) plus carrying a 3 yo whos kicking my stomach because he wants to play with 7yo. Get them in store and she acts up the whole time. Causing him to knock down multiple items over and over. My sister didnt care had me do it all while she talked to the guy about the grooms tux ( he already done his ) while i waited for my sons to get done. Guy couldnt do it because she kept talking. So i waited 45 mins to have a 3min measurement done. The 7yo kept getting smart and pushing into my stomach when i told her to stop and move she did it again. Im 13 weeks but high risk so that pissed me off more. Am i worng for not liking her? She is literally the worst kid ive ever met and I've met some bad kids.