I say it Lee-a-daun( I spell it Liadán). That's the way Irish people would say it actually. It a pretty unusual name here though. I don't understand where the Lee-din prn comes from - they sound quite different in my accent. (It's one of my favourite girls names. I don't care for Lee or Dawn though so that's a problem for me.)
I imagine it would be prn Lee-a-dawn in the U.S.