Assuming she entered illegally, you could get married once she is 18 and be sure to have her return home prior to her 18th birthday and 180 days (not six months). You could petition for her as soon as you were married. If done properly, she would only have to be away for a few months before she would return with her conditional residence visa. Another interesting option is that she appears to qualify for Deferred Action for Childhood Arrivals, which could be used in combination with the...