There are 3 George Clarke's listed in the Griffith Valuation of 1855 for Galway.
George Clarke, Parish of Clonrush, Townland Furnace, Poor Law Union Scarriff tenant of Francis C. Sampson M.D.
5a house and land 23.1.35
5bcd 3 labourers houses
George H. Clarke, Parish of Moyrus, Townland Ardbear, Poor Law
Union Clifden, tenant of Thos Ayres
#40 house, outbuilding, land 11 acres 0 roods 6 perches
George Clarke, Parish of Oranmore, Oranmore Village Poor
Law Union Galway tenant of John Lynch
17/#5 Main Street house, outbuilding and yard
George Clarke, same information but tenant of Walter Blake
#4 land 34.1.22
All three are farmers.
There are many Clarke's in the telephone book Galway, spotted Oranmore at least once.
Are the family RC or Protestant?
The dates you give 1862 means any records for baptisms would be parish records. Abigail and George are reasonabily unusual names. However, Galway belongs to an Irish History
Foundation that has parish records on line. This Foundation is a not for profit but does charge fees. You can search with or without parents names, or with father George for 1844. A birth record will give you her mother Abigail's maiden name, parish/place and date. Once you have mother's maiden name you can search for all siblings including Jane.
I don't think she and her sister would be born exactly the same year (but use the same birth year) unless they are twins which is possible but you should have no trouble finding her either.
The RC Parish records are online with Ancestry.com but also on www.familysearch.org
- go to main page but scroll down the page to UK/Ireland then click on that, next page scroll down again to Ireland records. If they are not there then you will need to use the foundation records.
You can buy books that speak to the life of farmers and even specifically Galway. Try Eneclann the Geneology division of Trinity College. There are many books about Ireland.
ps I'm not sure but this request seems familiar and wonder if you go backwards on the message board for Galway that you might find inquiries about George Clarke.
Also although your inquiry is about Galway you are posted on the Clare Co. message board so you might want to post
again in Galway's message board.