If she turns out to be the Ann Mylrea who married John Kelly on 26 Nov.1844 in Malew it would certainly tie up all the loose ends very neatly! Kay, who were the witnesses? (Apologies if you have already posted this info.)

There may be a Presentment in 1819/20 (or if not found, 1821 or 1822), naming Mr Myrea of somewhere and the mother's name. But only available in the MM Library.

William Mylrea left a will! MYLREA, William 1823 Mal E 1 0106423.
I have had luck with illegitimate children being named in wills, although not always called that - just "my son [named]" or "my daughter ....", and sometimes "my daughter the child of...". The supervisors can be revealing.

Sue