“How widespread is this “needing certain GPAs to get into a major” thing? Mainly big state flagships? Ivies, too?”
At engineering schools like Purdue and Wisconsin students are admitted to a Freshmen Year Engineering program, and don’t choose a specific major until the complete the first year engineering requirements. Once those are completed, you have to apply for a major, and different majors have different gpa hurdles, depending on capacity and demand.
At Illinois, you are admitted directly to a major, so DD has been admitted to ChemE. However, if she wants to change to a different engineering major at some point, that could be challenging because, strangely, Chemical Engineering is not part of the Engineering School.
Penn has 4 undergraduate schools: Wharton, SEAS, CAS, and Nursing. Transferring into Wharton is difficult, and transferring into SEAS is somewhat difficult. It is easier to move from Wharton or SEAS to The College. Nursing probably has the least movement due to specialization.
Cornell has more separate undergraduate schools than Penn, which increases the complexity of transferring. I think they had 9 schools, but I think that the business and hotel schools are consolidating. I am not sure of the exact number.
The point is that this is an issue at many schools, but it is not discussed much, which seems odd to me.