A Sarah Mitchell married in 1899 and this marriage is registered at Naas, so a good chance that this might be your Sarah. The only way to find out more would be to order a copy of the registration (similar info to that on an official cert). On that you would have her father's name.
If correct, then you could go on to find out more about her, using her married name.
I am taking a note that you have ORFORDs in your family. I have one as a Sponsor at a Baptism of a JOHN BREEN in 1841 and wonder if there was a family connection. JOHN BREEN's mother was formerly ANNE NOWLAN (from Castledermot). I am just mentioning these names in case you should ever find a connection.