Based on the 1851 census, in which she appears, aged 64, living with her daughter Eliza STOKES (nee BROWNING), Mary LOCK was born about 1787 in Tetbury, Gloucestershire.
The best fit for a christening is George and Elizabeth LOCK who christened a Mary on 10 Jun 1787 in Tetbury.
Mary married Isaac BROWNING in 1806 and they christened fourteen children, including 5 girls that were christened on the same day in 1829. It is extremely unlikely that Mary would have quintuplets, however the father of these girls was also a mason, and one of them, Charlotte aged 11, was living with Isaac and Mary in 1841. The girls were not born earlier and had a delayed christening because Matilda (Feb 1825) and George (Dec 1827) were christened promptly, and there was barely time for two pregnancies prior to Nov 1829, let alone five. The only other possibility is that some or all of these children were not Isaac and Mary's but their christenings sponsored by them. Apart from Charlotte, the children disappear from the record: they don't appear in census returns and no burials can be found. If they were quintuplets then they were unlikely to survive long.
Another mystery is the identity of George BOWMAN, a grandson, aged 7, living with Mary and her son Isaac in 1851. Ellen, the daughter of Mary's daughter Eliza is also with them. Who is George, and who are his parents? It's possible that "BOWMAN" was a enumerator's confusion of BROWNING, but why, if the other three members of the household are correctly named BROWNING? No marriage of a BROWNING and BOWMAN can be found.
Other information:
William Locke, of Longfurlong and of Dufton, baptised George 17571009, Richard 17600113, Isaac 17620207, Mary 17640827 and Thomas 17690618 in Tetbury. See http://www.oocities.org/elizajan/km/lock.html?201927