I am still up in the air on if there is a real advantage for acceptance involved with ED. If there is an advantage, and you only get one shot with ED, I think it is being wasted at schools like Duke & Vandy for an applicant with an UW GPA of 3.7 (regardless of the level of difficulty of her school).
Also, if your daughter is attending a private high school now, you are likely looking at nothing for aid from Duke or Vandy, so you are looking at an 80K+ annual price tag.