Here are some common and not-so-common Celtic names for baby girls:

Ailsa
An Anglicized version of a Gaelic form of Elizabeth (from Scotland's Ailsa Craig).

Aisling
The Irish word for 'vision.'

Aoife
From the Irish word aoibh, meaning 'smile' or 'good mood.'

Bridget
From the Irish word brigh, which might mean 'strength.'

Bryn
The Welsh word for 'hill.'

Cameron (f or m)
From the Scottish words cam, 'bent,' and sròn, 'nose.'

Caoimhe
From the Irish word caomh, meaning either 'gentle' or 'kind.'

Carys
From the Welsh verb caru, 'to love.'

Erin
From Eire, the Irish word for Ireland.

Gladys
From the Welsh word gwlad, 'country, nation.'

Gráinne
Possibly from the Irish word grán, 'grain.'

Gwendolen
From the Welsh elements gwen, 'fair, blessed,' and dolen, 'ring.'

Gwyneth
Welsh, either from gwen, 'fair, blessed,' or Gwynedd, a place name.

Kennedy (f or m)
One possible origin is the Irish word cinnéidigh, 'helmeted head' or 'ugly head.'

Maeve
From an Irish name that means 'intoxicating.'

Morgan (f or m)
From the Welsh elements mor and cant, possibly meaning 'sea' and 'circle.'

Morwenna
From a Cornish word meaning 'maiden.'

Niamh
From an Irish word meaning 'brilliance, bright.'

Nolwenn
From the Welsh phrase noyal gwenn, 'holy one from Noyal.'

Olwen
From the Welsh elements ol, 'track,' and gwen, 'fair, blessed.'

Orlagh
From the Irish name Orfhlaith, consisting of or, 'gold,' and flaith, 'princess.'

Rhiannon
The name of a Welsh goddess, probably from a Celtic word meaning 'feminine reigning [spirit].'

Reese
From the Welsh male name Rhys, which means either 'enthusiasm' or 'ardor.'

Talulla
From the Irish words tuile, 'flood, torrent,' and flaith, 'princess.'

Vaughan (f or m)
From a Welsh surname meaning 'small, little.'