Unfortunately the Tasmanian marriage record on the index only lists her age as Adult
BROWN John
MCGOVERN Sarah
20 May 1850 Age Adult
Registration Place Hobart
Reg#224/1850 Ref RGD 37
but her death record details her age
BROWN Sarah
No parents noted.
12 Jul 1889 Aged
61 years Registration Place Hobart Reg# 661/1889 Ref RGD 35
No parents names on Tasmanian marriage registrations until c1897.
Is your Sarah this convict transported from Dublin Ire?
http://search.archives.tas.gov.au/default.aspx?detail=1&type=I&id=CON41/1/19Her conduct record is on digitised page 88. I note in the margin of the record a note....14.8.50 Mar 24.8.1850 CP.
Further searching reveals she is

Permission to marry
http://portal.archives.tas.gov.au/menu.aspx?search=5McGOVERN Sarah Kinnear
BROWN John Ratcliffe 30 APR 1850 CON52/3 p27 RGD37/9 :
1850/224http://portal.archives.tas.gov.au/menu.aspx?search=1145519
McGovern Sarah
Departed 16 Jun 1848 from Dublin
07 Oct 1848 Ship Kinnear (2)
I can't see in the records that she was actually born Dublin. Of course you may have other information.
I think the Tasmanian Archives have provided a wonderful service with the digitising of the convict records.
I only intended doing a short post to give her age in the death registration...sorry if you think I got carried away

Cheers and good luck with your search.
Cando