There is a Mary Batchelor death in Hemel Hempstead district Oct-Dec 1855 (too early for age at death to be on the GRO index) and another one Oct-Dec 1872 age 73. I can't see her in 1861 or 1871 though, so maybe the 1855 death is her.
Her first marriage is on hertsdirect.org and you can view it for £5 if you haven't already seen it.
https://www.hertsdirect.org/ufs/ufsm...d=HALS_INDEXES