Looking at these entries, Margaret may have died in childbirth. ( Abergavenny is the correct registration district for Bedwellty.)
Births Jun 1839
HAMBLEY Mathew
Abergavenny 26 55
Deaths Jun 1839
HAMBLEY Margaret
Abergavenny 26 35
HAMBLEY Mathew
Abergavenny 26 39
The death cert would give her age at death, and the name/address of the informant.
Rambler