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You are legally permitted to this, based upon the information you have provided but should be aware that the amount expended will be taxed to her. If both you and your daughter can live with this (knowing that you may end up subsidizing her tax cost) it may be a great idea. I would caution you to be aware of where she is going. Africa is a large place and not all the populace there is friendly to Americans. Volunteer projects are wonderful learning and growing experiences for her and can help the local people but, if the area is dangerous, is it prudent for her to be at risk?
Thanks for the information and advice. One question of clarification. From your response I'm gathering that it is legally okay for me to use 529 funds for this given that it relates to her ability to get academci credit for the trip/progam given that she's a full-time student, but that the amount that I'd contribute towards the trip/program from the 529 account is taxable income for her? Am I understanding this correctly?