I've found a birth for a Sarah Cranch not too far from where you're talking about.
Sarah Cranch
Baptism/Christening Date: Mar 1808
Baptism/Christening Place: ROMFORD,ESSEX,ENGLAND
Father's Name: Richd. Cranch
Also found a marriage between Sarah and Thomas.
Sarah Maria CRANCH
Spouse: Thomas James BOARDMAN
Marriage: About 1841 Of Kennington, Lambeth, Surrey, England
Obviously the date is out though......but the area corresponds with the above birth place and also with the births of some children I found...so? maybe have a little bit more of a look into that?
eg. William Cranch Boardman
Baptism/Christening Date: 13 Jul 1836
Baptism/Christening Place: Brixton-St. Matthew, Brixton, Surrey, England
Father's Name: Thomas James Boardman
Mother's Name: Sarah Maria