The identity of Mary as the mother of Charles Russell is reasonably certain within the constraints of the records available online.
This means she was the wife of Richard Russell and her maiden name was Stringer.
The earlier details come from the fact that there is a Mary Russell in the 1851 census  who was from Wighton, that Richard and Mary married in Wighton and that there is a suitable baptism for Mary in Wighton.
However, the dates are out by a few years.
Richard and Mary seem to have six children. If the identities are correct then two were named after Mary's parents (Martha and Peter) and two were named after Richard's parents (John and Amy). The other two being Ann and Charles.
  

A search of the death index reveals several possible entries.
There is a burial at Burham cum Ulph 29 December 1854. I obtained the death certificate for this but she is  said to be the wife of John Russell, Blacksmith. She was 76 which means she was born about 1778.
However, if this is the Mary Russell who appeared in the 1841 and 1851 census then her husband had been dead for some time.  It is possible that the informant got the name of her husband wrong.
  

Searched for Mary in 1851 census.  Found one possible aged 76 born in Wighton. Assumed this is the correct Mary.

Searched for Mary in 1861 census.  Find My Past returned one, but the name has been transcribed incorrectly.
Therefore it appears that Mary died between 1851 and 1861. 

Searched for Mary in the 1841 census born 1775 plus or minus 5. Three found, but only one in the right part of Norfolk.
Assumed that this is the correct Mary.