so she is a US citizen and applying for you. all the hardships need to be to the US citizen. They do not care if you have a brother here and will miss him. If she is the US citizen you need to show why she can not live in brazil and why she needs you physically with her here in the us. does she go to school? did you help pay bills? have her father write a letter that she needs to stay in the us and what she does to help him, like take him to check ups, take care of him, pay bills for him. If she is the us citizen than she should sit done and brainstorm in all the ways she will be affected. does she have outstanding loans. dangers in brazil due to crimes, poor healthcare, her job her could not be praticed in brazil. She should come to the site and read the example letters and take a few hours to think about all the ways she would be affected without you here and if she went to brazil.