Interesting that own of the children was Clayton. I noticed this Mary Richards in 1871 who is living with her uncle Thomas Clayton in Bryn Shropshire in the Reg District of Oswestry
Thomas Clayton 69 Widowed Grocer Llanyblodwell, Shropshire
Mary Richards 19 Niece Housekeeper Llangollen, Denbighshire
Elizabeth Jones 14 Servant
Kay
Added -In earlier census years Thomas Clayton's wife was Margaret b 1802 Manafon, Montgomeryshire and I think this is their marriage with Margaret's surname Richards
https://www.familysearch.org/ark:/61903/1:1:NKCJ-2P2Interesting that in 1861 Thomas and Margaret had a servant Jane Ann Richards born 1845 Llangollen that could well also be a niece of Margaret's.
In 1851 I think this is Jane Ann Richards and family ( living in Llantysilio, Denbighshire) with father Thomas Richards also born Maenafon, Montgomeryshire as Margaret Richards/Clayton At the moment I can't see the family in1861 but note there is a 5 month old Mary Rikards/Richards! Could she be your Mary Richards??
Thomas Richards 44 Maenafon, Montgomeryshire Fuller
Jane Richards 39 Eglws Fath, Cardiganshire
Josua Richards 17 Welshpool, Montgomeryshire
James Richards 15 Welshpool, Montomeryshire
Thomas Richards 11 Oswestry, Shropshire
John Richards 9 Llangollen, Denbighshire
Jane Ann Richards 7 Llangollen, Denbighshire
Margaret Richards 3 Llantysilio, Denbighshire
Mary Ricards 5 Months Llantysilio, Denbighshire