Am I wrong for not babysitting my niece anymore?

I told my sister I'm not babysitting my niece anymore. She's 8 almost 9 and the most disrespectful little girl I have ever met. My sister doesn't believe in punishments. She believes in talking it out. I don't have kids so maybe I don't understand but all shes done was teach her daughter to manipulate her and be a little brat. I don't believe JUST talking with NO CONSEQUENCES at all works! In the real world you get consequences and she doesn't punish her. This girl has been kicked out of her school which is why I agreed to babysit, but she cusses at me and tells me she's not gonna do something. She likes to abuse my cat and when I tell her to stop she calls me a bitch. Last week my sister was mad her daughter got scratched by my cat and I honestly didn't give a duck. She continued to torture my cat. When I put my cat in my bedroom she went into my bedroom and pull her tail and yank on her. I yelled at her to stop and she cussed at me. As I went to take my cat from her my cat scratched her arm. My cat has all her shots so she'll be fine. Honestly it was very deserved. I had her yesterday and she got mad because I wouldn't let her have any sweets since we were about to have lunch so she went and threw my $700 laptop across the floor, shattering the screen. I called my sister at work and told her to come get her daughter. I told her I'm not babysitting her anymore and she said "What am I supposed to do? What about my job?" I told her straight up her daughter is disrespectful and I'm not doing it so she will have to figure something out. She has a damn baby daddy too, but she's a bitter baby mama who doesn't want him involved because he doesn't want to be with her so they are in a custody battle. I tried to help her and she's lucky I'm not demanding she replace my laptop.

Edit: I know you guys think I should make her replace it, but she doesn't have the money so I would be waiting a very long time for a new laptop and I need one now for school, so it will be easier for me to just take some money out of my savings for a used one.