Having failed to find evidence in a census of the survival of Stephen MERRITT junr post-1851 and Lucy post-1861, it looks as if only the NORGATE children of Catherine married and produced children, unless you know different? As the NORGATE boys were settled into marriage and appear regularly in consecutive censuses, it's feasible that Catherine may have joined her married daughter, but I can't find any trace of a likely Catherine/'Caroline' FOSTER in the UK born France until 1881, by which time it's likely that Catherine senr had died.
I think the only way forward is to seach the Bramdean Burials PR 1854-1863 to ascertain which of the MERRITTs, if any, feature. Having regard to the variant spellings of the surname, I've noted deaths of 3 Stephens [1854, 1856 and 1862] and 1 Lucy [1863] in Alresford Regn District. I'll put them on my 'to do' list for my next HRO visit and, if applicable, delve further into the later burials.
Update: Found daughter Catherine FOSTER 1861; 1871, 1891, 1901. If you send your email address via PM I'll provide references. Still no sign of Catherine senr post-1861.