Catharine was born in 1792. She died at the age of 59 in 1851 in Lowton.1
Death Notes
Two deaths for "Catherine" mather appear to be others. This death for "Catharine" Mather is a good fit with correct and less common spelling of Catharine, and they did marry at Leigh.
Lancashire Death indexes for the years: 1851 MATHER Catharine 59 Lowton Wigan & Leigh LOW/6/101