HI
The North Wales BMD has only one Sarah - 1838, Ruabon Sub-district
GRO index is Dec Q, 1838, Wrexham vol 27 page 242
There is only one baptism entry for a Sarah at St Johns, Rhosymedre (which was part of Ruabon Parish until 1844) . It's a bit later but it might be a possible late baptism:
23 Sept 1845 d/o Thomas Leonard (mill manager) and Margaret. Abode - Acrefair
If this isn't a late baptism, the family could be non-conformist and not show in the parish records.
Gadget