Your indication that the death notice of Mary Ann (Littledyke) GRIGG (d 17 Nov 1845) appeared within the Palmyra Spectator on 20 Nov 1845 is very helpful!
I have seen the 17 Nov 1845 date of death given in various online posts, but had never before seen any authority for this date.
The Historical Society of Missouri doesn't seem to have digital copies of the 1845 papers online. Are you in Marion County? Does the Palmyra or Marion County Library or a local Historical or Genealogical Society have the microfilm for this edition of the paper?
Is there a published book of Marion County death notices which contains the abstract you mention? If so, what is the title of this book?