I am being warned there are more replies pending but anyway I have seen two probably siblings of Elizabeth on the PRONI indexes. First is Edward born 1921 and second is Mary born 25 Sep 1923. Due to spelling variants I used begins with "Mag" for mothers maiden name. Mary's birth is under magennes.
I can now say thanks to Softly Softly, I’ve finally got the correct person. The birthdate on the death certificate was indeed wrong,and should have been 21st June 1919.So Elizabeth’s mother was Annie Maginnis, and her father Patrick McKeown.