Sitting in on classes at SLAC's and Tufts, Northeastern, BU during visit - is it a thing?

DD26 will tour colleges in New England this April. She would love to sit in on a class or two as part of the visits. Has anyone’s kid had luck cold-emailing professors to set this up? She can’t find any process for this on the school websites but we’ve heard rumors that students do this.

TIA!