Please tell her now that Duke will be a severe financial burden on you (for retirement) and her younger siblings (for their college funding) and that it would only be realistic if she got a large merit scholarship (very rare).
Do not be like this parent who said that “money is not a factor in the decision” in the 11th-12th grade summer and allowed and encouraged the student to make a list of mostly expensive colleges:
http://talk.collegeconfidential.com/college-search-selection/1789885-best-schools-for-math-comp-sci-with-undergrad-research.html
But later did not want to pay for cost of the student’s first choice college which is similar in cost to most of the other colleges in the application list:
http://talk.collegeconfidential.com/parents-forum/1866912-need-advice-on-college-choice-etc-p1.html