Your older daughter is a senior and you're just figuring out now that room and board is a 529 qualified expense? Wow.
529 money, like scholarships that are tax-free, is "tax advantaged," meaning that money from a 529 that pays for AOTC qualified expenses cannot be used to claim the AOTC. You should, however, still be able to claim part of the scholarship that pays for tuition as taxable income, so that you can claim the AOTC based on that amount.
529 funds that pay for room and board are not taxable, as long as they do not exceed the school's published COA for room and board or the actual amount charged by the school, if the student is residing in housing owned or operated by the school.