I highly recommend Bryn Mawr.
Also, Temple University. Dr. Elizabeth Bolman would be perfect for what you want to study. She focuses on Coptic art but overall she is a great mentor for anyone interested in Early Christian art. I had the pleasure of studying under her and she is AWESOME http://tyler.temple.edu/faculty/elizabeth-s-bolman-phd
She actually studied at Bryn Mawr and quite a few of her grad students were Bryn Mawr alumni.
I'm also considering graduate studies in Early Christian art and I'm looking into conservation programs.
Edit - I made an account just to post this fyi. So you know how excited I am on this subject!
