I echo everything that @collegemom3717 has said.
All of William & Mary’s upperclassmen dorms now have AC to my knowledge. A couple of the freshman dorms: Lemon, Jefferson, and Yates have AC in the rooms as well. If you are dead set on living in a dorm with AC, you can try to mark that you would prefer a larger dorm in your housing preference survey – which in most cases they do have AC.
I lived in a freshman dorm without AC, and like collegemom said, it is completely fine. It does get rather warm during the first month and last month of the year, but all the communal spaces and other parts of campus have AC. It allowed for a bonding experience and we spent much of the time together in communal spaces, and just had fans in our rooms. You can also get approval to get a window AC unit installed in your room (just get a doctor’s note), which my roommate did – but by the time that happened it was already cool enough to not be an issue at all.
This certainly shouldn’t be a deciding factor, and if there is a medical condition where this is a requirement, let W&M know and they will do their best to accomodate. In the past, I have defended W&M on this particular issue, but I do think it is about time that they modernize all the freshman dorms in this regard. W&M is certainly not the only campus facing this though, I know a couple of other campuses are facing the same thing.
As someone else from the Northeast, your student will definitely find their home here if everything else is a fit. Happy to also answer any other questions as well, I previously answered some questions about the school here: Ask questions about William and Mary here