Thank you, again, Helmut!
Schäfer is the surname found on death records for some of Margaretha's children. But as I have not yet located her marriage record, I am still unsure what is her correct LNAB.
You are right about Kettenring - that is the correct spelling. I have occasionally seen it as Kettering and in much earlier times it was spelled Kettenrinck.
I have found a birth record for Francisca Margaretha Brügel born 20 Jul 1787 in Zeselberg to Michael Brügel and Elisabetha Hahn - I do not know if this is the same person as who died in 1859 or if this was an older sister. I am thinking she may be a sister who died young. The Wallhalben parish where most of their children were baptized seems to not have records for the period 1799-1816 (a son, Valentin, was born in 1802 and I have also not found his birth record).