I have also just find the family in 1891.
The Mother-in-law entry seems to have an additional inital tacked on and seems to appear as "Mary Couch G".
Although this type of entry seems much later than I might have expected I would consider the possibility that "mother-in-law" might actually mean "STEP-mother". (Unless, of course, Anna Mary had been previously married in which case WALTERS would have been the name of her first husband.)
1891 Census, Camborne
20 Bassett St
William Hy Cocking, head, mar, 45, tin miner labourer, Illogan
Anna Mary Cocking, wife, mar, 34, Crowan
Mildred Mary Cocking, 12, scholar, Camborne
Edwin Stanley Cocking, 10, scholar, Camborne
Thomas Norman Cocking, 9, scholar, Camborne
Evelyn A K Cocking, 7, scholar, Camborne
Sydney(?) Garfield Cocking, 5, scholar, Camborne
Christian I(?) Cocking, 3, Camborne
Frederick George Cocking, 11 mths, Camborne
Mary Couch, G Mother-in-law, 74, living on her means, Crowan
In the 1881 Census William Henry Cocking is at Redriver Roskear Crofts, Camborne with wife Anna Mary and two children - Mildred M. (2) and Edward Stanley (11 mths).
1871 Census, Camborne
Roskear Crofts
William Cocking, head, mar, 50, tin & copper miner, Illogan
Grace Cocking, wife, mar, 49, Camborne
Nicholas J Cocking, son, unm, 28, tin & copper miner, Camborne
WILLIAM Cocking, son, unm, 25, tin & copper miner, Camborne
Thomas Cocking, son, unm, 23, tin & copper miner, Camborne
Stephen Cocking, son, unm, 18, tin & copper miner, Illogan
Ann Cocking, daur, 14, scholar, Illogan
Catherine Cocking, daur, 11, scholar, Camborne
James Cocking, son, 7, scholar, Camborne
You may DISREGARD part of my comments above regarding Mary COUCH as I believe I have found the answer.
1871 Census, Crowan
Polcribo
Mary Couch, head, mar, 54, stone mason's wife, Crowan
Anna Mary Walters, g'daur, 15, scholar, Crowan
** So the Mary Couch G is incorrect **
In fact (and it did cross my mind) the G is written in such a way and position as to be confusing and the entry actually reads "Grandmother-in-law". ;D
This means that Mary Couch had a daughter who married someone named WALTERS who were then the parents of Anna Mary.
Mary Couch was living next to the family if Samuel and Christian Walters but, as Samuel was also aged 54, the only possible relationship might be that Samuel was an uncle to Anna Mary.
Have just tried a search of the 1861 Census for Cornwall and, currently, cannot find either family.
Before moving back to 1851 I decided to do a search for Mary COUCH and guess what
- I have now found Anna Mary Walters.
(The way her name is written I am sure it will have been indexed as WATTERS!)
1861 Census, Crowan
Polcribo Moor
Thomas Couch, head, mar, 62, stone mason, Constantine
Mary Couch, wife, mar, 44, Crowan
Ann Mary Walters, daur, mar, 24, miner's wife, Crowan
Mary Couch, daur, unm, 20, dress maker, Crowan
Thomas Couch, son, unm, 17, stone mason, Crowan
Edwd Couch, son, unm, 14, miner, Crowan
Anna Mary Walters, g'daur, 5, Crowan
1851 Census, Illogan
Tuckingmill
William Cocking, head, mar, 29, copper miner, Illogan
Grace Cocking, wife, mar, 28, Illogan
Elizth Cocking, daur, 7, scholar, Illogan
William Cocking, son, 5, scholar, Illogan
Thomas Cocking, son, 2, Illogan
Mary Cocking, daur, 1, Illogan
And now I will jump forward to 1901 to see what I can find.
1901 Census, Camborne
11 Church St
William H Cocking, head, mar, 55, coachman domestic, Illogan
Ann M Cocking, wife, mar, 45, Camborne
Mildred M Cocking, daur, single, 22, Camborne
Thomas R Cocking, son, single, 19, tin miner, Camborne
Sydney G Cocking, son, single, 15, tin miner, Camborne
Christian I Cocking, daur, single, 13, school, Camborne
Frederick G H Cocking, single, 10, school, Camborne
James A Stephens, boarder, single, 27, assistant medical practitioner, Scotland
Hope this lot helps you and please feel free to request any further information I might be able to help with.