But don't you already have a
Niamh? As a mn? With so many gorgeous other names to choose from, I wonder why you would repeat the name / sound.
If I had a dd tomorrow, she'd be
Niamh, so I do understand the attraction for the name. But I think it's time to expand your baby naming horizons a little.
How about
Isolde? Everyone thinks of it as a
German name, from the Wagnerian opera
Tristan und
Isolde. But it originated in
Ireland. Or
Isibeal? It's Irish for
Isabel and pronounced "ISH-bale." Beautiful, but probably not the easiest name to live with, I'll admit.
Eibhlin, "EEV-lin," I think, but check on that pronunciation.
To honor your English and Irish roots, personally I think keeping the names in tact and honoring their spellings is the way to go. A mixture of an English first name and an Irish mn, or the other way around? But that's just my two cents. :-)