Here's the Gaelic of the part that Lisa sings:
An Cailín Álainn (Thomás Mac Eoin)
Tá cailín álainn a dtug mé grá dhi,
Sí is deise is áille ná bláth is ná rós.
Gan í ar láimh liom is cloíte atá mé.
Ó a chailín álainn is tú fáth mo bhróin.
Curfá:
A chailín álainn a dtug mé grá dhuit,
bí ar láimh liom mo mhíle stór.
Abair liomsa gur tú mo ghrá gheal,
's beidh orm áthas in áit an bhróin.
And the English of that same part:
The Beautiful Girl (translated by Liam Hart)
I fell in love with a beautiful girl,
Who is as pretty as any blossom or rose.
Without her on my arm I am devastated.
O beautiful girl, you are the cause of my sorrow.
Chorus:
O beautiful girl that I love,
Be on my arm, my great treasure.
And tell me that you are my bright love.
And I will have joy in place of sorrow.
Source (and the rest of the song) here:
http://www.liamhart.org/cd/#l3