my oldest babies look a like but are not alike

Kristyanne
Ok so lately Iv been questioning so much about life and my children these are my two oldest 
Elizabeth 8 
And Bella 5
Elizabeth is a beautiful respectful child plays with kids from all races ect 
Bella started school 10 months ago and has been in trouble a lot for picking on a black child Iv sat down spoke with her and explained we are all the same ect she told the other girl she couldn't be friends because she had ugly skin :( and that means she is ugly ect I feel so ashamed right now what am I doing wrong we have aboriginal in my family the schools treated me like she was getting it from home but she shore as help isn't (what am I doing wrong am I failing her ? I just don't know anymore am I looking to much into it because I'm pregnant and emotional?)
How can I raise one child to be so respectful but another to be a bully 
Sorry had to rant I just feel like I'm a bad mum right now