I have checked my Mayflower 5 Generations book for a Mary Billington married to a John Williams.There are lots of Marys, but so far I haven't found one married to a John Williams.I will keep looking.
I joined the Mayflower Society using John Billington as my Mayflower Ancestor.
This is what the 5 Generation book says about John's wife, Elinor. (Elinor is found spelled about 3 different ways, besides her being called Ellen or Helen):
They list her birthplace at perhaps Lincolnshire, Eng.ca.1580
Her second marriage to Gregory Armstrong at Plymouth, was between 14 & 21 of Sept. 1638.
She was still alive on 2 March 1642/3 because at that time her son, Francis Billington of Plymouth, sold 3 lots of land at Plain Dealing within the township of Plymouth: provided that Ellinor the wife of Gregory Armstrong be allowed to occupy one of the three said lots during her lifetime.Marilyn