Hereford,
Have you a death certificate for her, it might name her parents.
Without the parents it would be very difficult to identify the correct Winefred Heffernan.
that is all I can think off.
online only some parish records covering the 1820s will be searchable. the real south of the county around Cahir, Clogheen, Clonmel and the north of the County, no online database will give the Cashel and Emly diocese parish records which covers a large part of the county.
and some parish records will not go back to 1820 so you need the parents names to pinpoint where she was from.
Cecile