My cousin said I'm bad because I don't treat my niece and nephew like my kids

My niece was over for a sleepover but was being terrible and a bully to my daughter so I had my brother pick her up. She has since apologized and made it up to my daughter by having a girls day so they are good now. My cousin didn't agree with me sending my niece away since she's "pretty much my daughter". My brother is bi and married to a man. I carried their twins for them. But they aren't my kids. They aren't even biologically related to me. My cousin asked me did I really not see them as equals to my kids. I said no. Because they aren't my kids. She told me how could I say that after carrying them inside me. I said I believe we may have a stronger relationship than the average aunt nephew/niece relationship but no I don't have them on the same level as my kids. They aren't my child biologically and I didn't raise them. There was a point where I only saw them on Holidays because my brother and BIL moved. It was emotional when I had them and had to give them to my brother but I know what I am in their life. I'm their aunt. My cousin thinks I'm so horrible because I don't see them as my children and hold them to the same place as my kids. But they aren't mine so why would I? I'm their aunt and was a surrogate.