Help! I made my 11 year old sister cry

I’m 20 years old and the guardian for my lil sis. She just started secondary school (for those in the US it’s like starting middle school I think) and when she came home today I asked how her day was. It’s only her second day at this school. She told me she made this friend Bella who doesn’t like this girl called Lacey and that Bella told her to make fun of Lacey so she did. She went up to this girl Lacey and asked if she wanted to play with them, and then when Lacey said yes my sister laughed in her face and said well no you can’t.

I got mad at my sister for being friends with a bully and told her she shouldn’t be friends with girls like Bella even though she said Bella is nice to her she said she likes Bella because she’s ‘cool and popular.’ I tried to explain to my sister that it doesn’t matter how nice Bella is to you if she’s mean to other people and is encouraging you be mean too then you should drop this girl and not be friends with her. I basically made her cry because I think I made her feel really bad about herself so she ran off upstairs. I know she’s not a bad person I feel so bad now I never want to see her cry or be the reason I just wanted to explain to her that that kinda behaviour is not okay but I think I was too harsh. Please someone help me! What can I do or say to make her feel better? I know my sister isn’t a bully she only did it for validation from this Bella girl and now I’ve really upset her for accusing her of being a bully cus I said she’s just as bad as Bella for making fun of that girl. How can I fix this? What do I say?

Edit: thanks everyone who commented! I was starting to doubt myself but thanks to you guys I now feel confident with what i said. Bullying is never okay and I had to let her know. She’s not crying anymore but still a lil sulky, watching Sam and Kat whilst I make Thai green curry yum!