Hi, Just found this post, I think my 3x greatgrandad George Beer could be Mary's brother.
I have just found on the Cornwall parish registers for births, to James and Mary Beer, as hepburn said earlier..
William b Oct 6 1816 ID 909804 residence Harrowbeer.
John b March 29 1818 ID 909940 Harrowbeer.
Mary b Jan.2 1820 ID 910111 Metherill.
Richard b Nov. 18 1821 ID 910289 Metherill.
Thomas b Sept 4 1825 ID 910620 Metherill.
George b July 16 1827 ID 910759 Metherill.
Eliza b Dec. 25 1828 ID 910877 Metherill.
I am not sure if these are the siblings of George, as I only had him before reading your post, and I am still fairly new to researching.
George married Jane Gumb and moved to Scotland with his family, and his daughter Mary was born Sept 3 1867, Glassford Lanark, IGI extracted, father George Beer mother Jane Gum.
George and family moved again, to Staveley, Derbyshire,but on the 1881 census, it has Mary born in Stravon, Scotland.
I am not sure where James came from, Cornwall, or Exeter, Devon. I have no further information on him, or Mary Husband.
It can be so confussing but I keep trying.
Any help or more information is greatly appreciated.
Hope this helps larky.