I love this name (pron. mur in ) with its celtic connections as I am scottish and I also love Willow, Im 16 weeks pg and convinced i'm having a girl, find out for sure next week. Which is nicer, please do not comment neither as its not helpful.
I would have loved to use the name Muireann (know a few people at home in Ireland with the name) but we pronounce it M-wir-an and dp just couldn't say it properly and I didn't think many other people in England would either.
Muireann is lovely. Wouldn't worry too much about the spelling and pronunciation. Usually people only have to be told once and if someone can't be bothered to get it right then that is their problem. All the important people in her life will know her name and say it properly.