I can ask a few old people near Innishannon if the name rings any bell with them.
In the meantime I would suggest requesting a Marriage Cert for Catherine Mcnamara and Michael Holland. One would assume they married abt a year before first child was born and you have a date for Eileen's birth. You could apply for a Marriage Cert (photocopy) at http://www.groireland.ie/apply_for_a_cert.htm
You don't need exact data and of course there was no PPS numbers then. Of course they may not have married in Innishannon and I don't see amy Michael Holland or Catherine McNamara names in the Census of 1901 or 1911 with an address which would be anywhere in the broad Innishannon area. I think it is worth trying and using County Cork as the marriage location - very vague but those surnames are not real common ones