Sarah Alcock probably born 1814= 1817 gleaned from the census. Attempting to find where the Alcocks lived in Ireland at that time is difficult and yet knowing that Alcock might be her married name. I searched the Tithe Applotment Books as the nearest record in time.
I have arranged the results by County. by county .Special note I was astonished at the amount of entries for Edward J Alcock. Is it a prank or error? So for brevity in this reply having found 126 entries in total I have reduced them by 57 lines as follows
23 entries for Alcock Edward J Durrus Cork 1830 down to one
10 entries for Alcock Edward J Kilcrohane Kilcrohane Cork 1831 down to one
24 entries for Alcock Edward J Kilcrohane Cork 1831 down to one
Tithe Applotment Books in 6 counties http://www.irishgenealogyhub.com/Alcok, Geo.-T[ownland]l: Fully Yr: 1834-Inishmacsaint –Fermanagh
Alcock, Joseph-- Townland: Drumnot Year: 1825-Killyman-Tyrone
Tithe Applotment Books in 26 counties 124 entries see
http://titheapplotmentbooks.nationalarchives.ie/search/Alcock William Corbally Corbally Cork 1833
Alcock E I Drinagh Cork 1833
Alcock Wm M Drinagh Cork 1833
Alcock E J Durrus Cork 1830
Alcock Edward J Durrus Cork 1830
Alcock Arrean Kilbrogan Cork 1827
Alcock Maskelyne Roughgrove East Kilbrogan Cork 1827
Alcock Maskeyline Roughgrove East Kilbrogan Cork 1827
Alcock M Roughgrove West Kilbrogan Cork 1827
Alcock Maskelyne West Roughgrove Kilbrogan Cork 1827
Alcock Kilbrogan Cork 1827
Alcock Edward J Carravilleen Kilcrohane Cork 1831
Alcock Edward J Carravilleen Kilcrohane Cork 1831
Alcock Edward Jones Durrus Kilcrohane Cork 1831
Alcock Edward J Fahane Kilcrohane Cork 1831
Alcock Edward J Farranamanagh Kilcrohane Cork 1831
Alcock Edward J Glanlough Kilcrohane Cork 1831
Alcock E F Kilcrohane Kilcrohane Cork 1831
Alcock Edward J Kilcrohane Kilcrohane Cork 1831
Alcock Edward Jones Kilcrohane Kilcrohane Cork 1831
Alcock Edward Jones Kilcrohane Kilcrohane Cork 1831
Alcock Edward J Reenacappul Kilcrohane Cork 1831
Alcock Edward J Rossnacaheragh Kilcrohane Cork 1831
Alcock Edward J Rossnacaheragh Kilcrohane Cork 1831
Alcock Edward J Kilcrohane Cork 1831
Alcock Thomas Killoran Killoran Galway 1828
Alcock John Castlecomer Castlecomer Kilkenny 1823
Alcock John Donagile Castlecomer Kilkenny 1823
Alcock Dunkitt Dunkitt Kilkenny 1825
Alcock Strangsmill Dunkitt Kilkenny 1825
Alcock W Nicholastown Kilcolumb Kilkenny 1829
Alcock W Nicholastown Kilcolumb Kilkenny 1829
Alcock Nicholastown Kilcolumb Kilkenny 1829
Alcock Nicholastown Kilcolumb Kilkenny 1829
Alcock Nicholastown Kilcolumb Kilkenny 1829
Alcock Nicholastown Kilcolumb Kilkenny 1829
Alcock Alexander Muccolee Muckalee Kilkenny 1833
Alcock Gardens St Canice Kilkenny 1828
Alcock Patt Doughloon Achonry Sligo 1827
Alcock Richd Doughloon Achonry Sligo 1827
Alcock Alexander Kilculliheen Kilculliheen Waterford 1833
Alcock Alexander Waterford Kilculliheen Waterford 1833
Alcock Killea Killea Waterford 1827
Alcock James Upper Grange St Johns Without Waterford 1835
Alcock Waterford St Johns Without Waterford 1835
Alcock H Carrigmacogue Clonmore Wexford 1834
Alcock H Carrigmacogue Clonmore Wexford 1834
Alcock H Coolteigue Clonmore Wexford 1834
Alcock H Coolteigue Clonmore Wexford 1834
Alcock H Crawn Clonmore Wexford 1834
Alcock H Crawn Clonmore Wexford 1834
Alcock H Donamore Clonmore Wexford 1834
Alcock H Donanore Clonmore Wexford 1834
Alcock Harry Kilgibbon Clonmore Wexford 1834
Alcock Harry Kilgibbon Clonmore Wexford 1834
Alcock H Killarah Clonmore Wexford 1834
Alcock H Killaray Clonmore Wexford 1834
Alcock Harry Park Clonmore Wexford 1834
Alcock Harry Park Clonmore Wexford 1834
Alcock H Wilton Clonmore Wexford 1834
Alcock H Wilton Clonmore Wexford 1834
Alcock Harry Clonmore Ferns Wexford 1824
Alcock Harry Clonmore Ferns Wexford 1824
Alcock A Fethard Fethard Wexford 1828
Alcock A Grange Fethard Wexford 1828
Alcock Freynestown Freynestown Wicklow 1836
Alcock Friendstown Freynestown Wicklow 1836
I regretfully think its almost hopeless to bridge the water without more information.