I searched the Irish Family History Foundation's database. It contains 12,000,000 surviving rcds for abt 65% of Irish counties. Rcds B4 1840 are sparse, B4 1800 rare. I only search the 65% which are.
For Catherine Sheridan B 1841 (exact) in Co. Cavan, I found 1 B rcd in 1841 in Killann parish. The father's name is Pat(rick). I did not find B rcds for her siblings. These events may not have been rcd'd, or didn't survive.
For a Catherine Sheridan M 1866 +/- 4 yrs, I found 3 M rcds for Catherine, but no corresponding rcds for Peter in Cavan, or the rest of Ireland. Could they have married in England?
Google the Foundation's name to lead you to the database. Register, opt to be notified as rcds are added and browse. Pls post your search results to my genforum msg.