Best option may be large state flagship honors colleges. Like attending a small college with all the benefits (and fewer administrative headaches) of a large university.
An important aspect of small classes focusing on discussion is to be among intelligent and motivated students.
P.S. I love AustenNut’s suggestions on this website, but any large state flagship university honors college will put your daughter in a different league for intelligent discussion. Classes are typically capped at 25 students, but it can vary by school.
P.P.S. Also, honors colleges at large state flagships offer special housing for honors students as well as other living/learning options that promote intelligent discussion among motivated students outside of class.