It’s just so annoying that people are exploiting a law that has absolutely no impact on students’ lives to further an agenda. If you were to attempt to dissuade someone from attending UNC based on HB2 that could be legitimate (because UNC is within the ambit of the law) but you simply cannot make the case against Duke (in good conscience).
Try to promote Grinnell by pointing out an area in which it is superior to Duke. If you cannot find any data to make a compelling argument in favor of Grinnell, let the OP make the decision that is likely to secure his/her family’s future. It’s one thing to tell a wealthy student to go to Grinnell even though he/she is likely to make significantly more money as a Duke graduate. It’s quite another to tell a student from the OP’s socioeconomic background to make a decision based on completely irrelevant factors. Specially if you know that he/she is likely to regret the decision when it’s time to get a job and support a family…