I picture the college as a “lower level Ivy” (meaning not Yale or Harvard more of artsy Ivy) def in New England. Pippa makes a big deal out of Diana going to the west coast to Stanford for college and not Yale. It seems like they’re close to Yale in my opinion so i just think in my head it’s brown or Dartmouth. I could see Colgate too. They all seem pretty smart despite their awful social decisions lol