Congrats! I'm not a medievalist but have medievalist friends at very good schools and most of them did their MAs/MPhils in Europe--that doesn't mean it's better to study in Europe but in your field in particular, I doubt it would be a disadvantage. I personally think it's really useful to understand how academia works outside of the US and Trinity College is a good school (plenty of people--me, for instance--have been accepted into good US programs with MAs from totally unknown universities. Also why not just take the year or two abroad if you can afford it--to be able to do Celtic studies in Ireland seems enormously useful.
Anybody apply for / thinking of doing a PhD in Medieval? Have any advice about good programs? The pickings seem pretty slim as far as late medieval art goes, besides architecture, that is.