Thanks for everyone's interest.
Valda - You may be right about finding Catherine (or Mary?) living with her daughter in law, however, my records show that Charlotte's mother just happened to be called Mary (born 1796 in Somerset) so it could easily be her. John Cabble, Charlotte's husband, is found living back with his father, Benjamin in this census so at least that might be explained if his wife was poorly/pregnant.
Other info I have:
John Cabble married Charlotte Corp (listed Carp in 1841 census!!) on 21 August 1859.
A Harry George Cabble was buried 12th March 1863 in Keinton Mandeville Church, aged 1 year 11 month - means born approx April 1861. So perhaps she lost the first baby.
John & Charlotte did have at least one child, George A, born in KM in 1864.
Daisypetal - Benjamin Warwick Cabble was my gggrandfather.
So back to 1861 entry, it's a toss up between either Mary Cabble (mother) born Som, or Catherine (middle name Mary?) Cabble (mother-in-law) born Hampshire. If it was Catherine, it explains her apparent disappearance.
I suppose it's not possible to get a birth record from the baptism details of Emily Ellen, is it? I am currently trying to contact someone who descends from a son of Emily Ellen, so see if she has anything concrete about Emily.
All the census records show Benjamin to be born in KM so the question of how he & someone from Hampshire gets together has to be answered. One explanation is that Catherine could have been in service nr KM. But then there's Emily Ellen. Even if Emily is his child, why would she have been born in Hampshire. I've checked the census for Cabbles in Hampshire, and yes there are one or two in/around Portsea area so that's another idea I had.
Well I'll throw this one back to you all for another chew!