I have never come across any instance of Cushla being used in
Ireland as a given name.
However - my great-grandmother used to call my mother "A cushla" and "Alannah"(a leanbh/child) as endearments. At the time(1940s/1950s)
Alannah was unheard of as a name in
Ireland. It has emerged as a name here in recent year though - an import from other English speaking countries(Katelyn is a similar case). I wonder if Cushla will follow suit?
I have never met an Irish
Colleen - though I have met a Dutch one - she was living here for a while.