Her guidance counselor should have the info on your state schools. Sometime this semester it would be a good idea for her to discuss things about which colleges should be on her radar.
How things are done depends on the school and state. Find out if students apply to majors or the university as a whole in your state. Your first step will be to look at the public university system in your home state- there may be one or more covering the public colleges. Then look at the different websites for admissions requirements and stats for entering students. That will give you an idea of whether or not your sister is competitive for any given school. Also check to see which engineering majors are available at schools and requirements for them. Ideally your sister will do this work with your guidance. SHE needs to own the process. Once she has been exploring some college websites patterns will emerge and she will gain expertise. There may even be some sites she dislikes and decides the school should be eliminated.