For some reason, only the mother (Sarah) is recorded on the baptism. It could be that this is another Sarah Mather and was unmarried, and possibly married Joshua Webster, a cabinet maker on 22 Aug 1819, just 2 weeks before Peggy was born, but then why use the maiden name?
7 Oct 1839, Margaret Mather, daughter of Isaac Mather, landlord, married William Garside, Cali Printer, son of Richard Garside, weaver, both from Edgworth, full age.
In 1861 William and Margaret (42 & 41) were at Doffer Fold, Radcliffe with Fanny (20), Sarah Ann (16), James (12), Elizabeth (10), John (7), William (5), Mary Ann (4) and Ellen (9mo). Also there were Margaret's brother Joseph and his wife and her father Isaac (65).