not sure if anyone else has come accross it.
Mary ann cottons daughter born just before her execution to quick manning is on freebmd
MARGARET EDITH QUICK MANNING (as christian name ) COTTON (as surname)
births march 1873 durham 10a 435
I cannot find her marriage under same name nor death.
Mary ann cotton had a brother about 3 yrs younger than her named Robert i believe . Marys father fell down pit shaft at Murton colliery and was killed when she was about 8 so a check on 1841 census might help, her father was Michael Robson
some of this i got from wikipedia, i checked it with other sources and most of it is correct.
As far as who adopted Margaret edith, i have no idea. i've tried looking for her on 1881 census with mary anns brother but no luck, mary anns step father was called george stott but she despised him so can't see him having her either as his wife was long dead.will let someone else3 look for her but i did however find an interesting article in sunderlandd echo, a local newspaper for the area mary ann came from
http://www.sunderlandecho.com/editors-choice/Fresh-evidence-could-clear-notorious.5378485.jphappy hunting