The American Opportunity Credit is a maximum tax credit of $2,500 on up to $4,000 of qualified education expenses; up to $1,000 of the credit may be refundable.
I assume that you are just talking about the refundable part of the credit, since your daughter and her husband do not pay federal income taxes and the amount you mention is $1,000. I don't think that the IRS would have any problem with the scenario that you describe. Whatever deal you make with your daughter to help pay her tuition in exchange for your daughter turning over to you money from a tax refund is none of the government's business.