Petty, Mary 1852 March West Bromwich 6b 341
This is an entry for a death which might be your Mary Petty. There is no age given on FBMD but you could order the certificate stating that you only want it if it is for an lady aged around 75. If it is the correct one it might give you some more information.
When making a posting like this it reallly helps if you give all the details of (in this case) the 1851 census so that people can see what the names and ages are.
I am a bit worried because you say that Deborah's husband is John so how does this check out?
1871 England Census
West Bromwich St,Oldbury
Name Age in 1871 Birthplace Relationship Civil Parish County/Island
Hannah Allwell 17 West Bromwich, Staffordshire, England Visitor Oldbury Staffordshire
David Hughes 19 Oldbury, Worcestershire, England Son Oldbury Staffordshire
Deborah Hughes 58 Oldbury, Worcestershire, England Wife Oldbury Staffordshire
Elizabeth Hughes 15 Oldbury, Worcestershire, England Daughter Oldbury Staffordshire
Henry Hughes 13 Oldbury, Worcestershire, England Son Oldbury Staffordshire
John Hughes 17 Oldbury, Worcestershire, England Son Oldbury Staffordshire
Susan Hughes 21 Oldbury, Worcestershire, England Daughter Oldbury Staffordshire
William Hughes 57 Burton-upon-Trent, Staffordshire, England Head Oldbury Staffordshire
Name Age in 1871 Birthplace Relationship Civil Parish County/Island
If that is the right Deborah (is John a mistake?) then she married in 1834 so you won't be able to use her marriage certificate to get her father's name.
Deborah Pettey; Spouse: WILLIAM HUGHES Family
Marriage: 26 JAN 1834 Saint Thomas, Dudley, Worcester, England
But sometimes the St Thomas entries do have details of the fathers and witnesses so it can be worth looking there.
I looked on the IGI to see children for Deborah and John and they seem to be quite different to these ones in the census, and these for Deborah and William are not there! Very confusing so I hope you have it all sorted out