I stumbled across the name Mavourneen a few days ago. I’ve heard the phrase it comes from before, an Irish phrase meaning my darling, but it was the first time I’d heard it as a name. I think it fits right in with the [name_f]Cathleen[/name_f]/[name_f]Eileen[/name_f]/[name_f]Maureen[/name_f] bunch with an original spark to it. Thoughts?
Also, combo suggestions? Thoughts on any sibsets? I was thinking [name_m]Cormac[/name_m], [name_f]Honora[/name_f], and Mavourneen together (and possibly [name_m]Eamon[/name_m], Fionnbarr, [name_f]Brighid[/name_f], or [name_f]Fiona[/name_f]).
My first thought was “please, no”. Apologies if that is blunt, but there are plenty of lovely names out there (including [name_f]Cathleen[/name_f]/[name_f]Eileen[/name_f]/[name_f]Maureen[/name_f]) that don’t involve using an old Irish phrase. I love Celtic names, but I think this would be really hard for a little girl to wear-- at least in the US. Suggestions below (which I imagine you’ve probably already seen if you’ve searched far enough to find Mavourneen) are just some of my favorites. I love the idea of [name_m]Cormac[/name_m] and [name_f]Honora[/name_f] 
Other ideas:
[name_f]Aisling[/name_f]
[name_f]Bridget[/name_f]
[name_f]Caitlin[/name_f] (another Irish version of [name_f]Katherine[/name_f] via the [name_m]French[/name_m] [name_f]Cateline[/name_f])-- anglicized version is [name_f]Kathleen[/name_f]
[name_f]Caitriona[/name_f] (Irish version of [name_f]Katherine[/name_f])
[name_f]Ciara[/name_f]
[name_f]Eileen[/name_f]/[name_f]Aileen[/name_f]
[name_f]Erin[/name_f]
Fidelma
[name_f]Fiona[/name_f]
[name_u]Keeva[/name_u] (Anglicized version of [name_f]Caoimhe[/name_f])
[name_f]Maeve[/name_f]
[name_f]Mairead[/name_f] (Irish form of [name_f]Margaret[/name_f])
Mairenn/Mairin (Irish diminuitives of [name_f]Mary[/name_f])
[name_f]Maureen[/name_f] (Anglicized version of Mairin)
[name_f]Moira[/name_f]/[name_f]Maura[/name_f] (Anglicized versions of [name_f]Maire[/name_f])
[name_f]Neve[/name_f] (Anglicized version of [name_f]Niamh[/name_f])
[name_f]Nola[/name_f] (diminutive of [name_f]Magnolia[/name_f] & [name_f]Finola[/name_f])
[name_f]Nora[/name_f] (short for [name_f]Honora[/name_f] and [name_f]Eleanor[/name_f])
[name_u]Rowan[/name_u]
[name_f]Saoirse[/name_f]
[name_f]Talulla[/name_f]
It would be pretty far out there in the US but maybe it could work if you streamlined the spelling a little? Mavorneen? Mavornine? Idk.
[name_f]Maeve[/name_f] is super popular and growing and, as you noted, it does bear a similarity to [name_f]Maureen[/name_f], etc. it also reminds me a little of [name_f]Lavender[/name_f].