I think I found a strong possible for your Mary Ellen Allen.
Below are the clues I found.......
Virginia Marriages, 1740-1850 Groom Name: Nicholas B. Allen Bride Name: Margaret A. Smith Marriage Date: 26 Oct 1846 County: Lewis State: Virginia
Tyler County is listed in Virginia not West Virginia for the 1850,1860,1870 census records I checked.
Peg or Pegy is a common nickname for Margaret.
Above Nicholas is listed on several TREEs as Nicholas Brady Allen bn 1825 Virginia s/o Solomon Allen & Elizabeth Brady
You will find Nicholas B.& Margaret Allen on the following census records: 1850 VA, Lewis Co 1860 VA, Tyler Co 1870 VA, Tyler Co, Union twp 1880 WVA, Roane Co, Smithfield The 1880 census states Margaret Allen's mother was born in Ireland.
They have a daughter listed as Mary or Mary A bn abt 1855 and this same daughter is listed as Ellen on one of the TREEs I found.
Check the marriage records link you have and see if any other Allen were married there and if so..........what were the names of their parents.With luck, one of her siblings that are identified 'clearly' on the census records, will list the same parents.At least you have something to work on now.
Hope something above will be of help. Good Luck Marsha