Patrick Flavahan/ Flavin

I am helping a friend who is trying to trace her Irish ancestry . She knows very little so this post will seem very vague . Her mother was a Mary Theresa Flavahan/ Flavin who was born in Ireland about 1942-1945 not sure where but think there may be a connection to  Waterford , she was in the UK  ( London ) where she married and had a child . Mary's father was a Patrick Flavahan/ Flavin who was a factory working according to Mary's marriage cert. She doesn't know what year he was born or who Mary's mother was . My friend has done her DNA with ancestry and has a strong match to Pascal Roche of Waterford , but I can't seem to find the connection . I haven't been able to locate Mary's birth cert as yet , the closest one has no father's name only a mothers name which was Ellen Flavahan  who was from Ballybricken  and Mary was born in County Home Dungarvan . It is possible that Mary made up a name for her father . Not sure where to go from here , so any suggestions or help would be much appreciated