I guess trying for second time is not a bad idea. Your sister should not change anything in her document and should speak truth about you. Since they are claming her that she can be a potential Immigrant, i think your sister should prepare some document which will make them clear that she will return bk to nepal, once her study gets complete eg: if she has any work expe and job gurantee letter after her return might help her.Or some family tie which shows them that she will return bk.Just make sure that she went through all those document which they have mentioned in their list,other than that if they asked for anything else while interviewing, she should be smart enough to reply them that those are the only document that is mentioned in their list. Tell her to be polite, soft, never argue with them. It is all abt luck.. there are so many people who gets rejected at first. So i think she will be alright. Gud luck.