Statutory recording of births only started in Ireland in 1864. So you won’t find a birth certificate for Agnes. You might find her baptism but to do that you’ll need to know her exact religion.
Details of the surviving parish records are on the PRONI website. Copies of the records are kept in PRONI in Belfast. RC records are also in the National Library in Dublin. Or you can order a copy in to your nearest LDS library. (The records themselves are mostly not on-line and you need to search the microfilm records).
www.proni.gov.uk/index/research_and_records_held/catalogues_guides_indexes_and_leaflets/online_guides_and_indexes.htmPage 141 for Clones.