Attaching snip of part of a baptism record from St Johns C of E at Parramatta.
I am doubting that Sarah's son, Phillip, was known by the surname PEMBER.
It is possible that the burial reference is NOT for Sarah's son, but on the other hand, it may well be him, it is indexed with the year as 1852.
.... NSW BDM has the burial as 1852 and as Volume 118, line 985, and as Phillip MURPHY, aged 29.
I can see on the NSW Coroner's Index that it has, in 1853, at item 7063, listed a Phillip MURPHY, accidently Killed and that locality is likely to read 'South Creek' although Ancestry seem to have transcribed it as ....
Lomsh Creek.

There is a date of 8 January (1853) associated with that entry, and the outcome of L C North's inquiry is dated 25 January 1853.
I rarely suggest anyone seeks to obtain a copy of the Early Church Records of the NSW BDM. They are scant on family history. But an official transcription of the 1852 document will include the date of burial and the cemetery and the denomination, and that info may lead to searching within that cemetery for his mother, and hopefully take our OP to Sarah.
South Creek, the locality, is a former name for Rev Marsden's landholding at Mamre, near St Marys near to the NSW State Archives facilities at Kingswood. South Creek, the water course, flows through today's St Marys and enters the Hawkesbury River near Windsor. landholders in the early to mid 1800s would refer to South Creek in a broad sense, so quite a large district, from say Narellan, through Badgery's Creek, St Marys, and onward north to Windsor.
JM