Thank you, Donna. If Martin were to find proof that Dora Mylchreest Quayle was his grandmother, then those MIs will be very useful.
Martin, if you look at the family tree section on Ancestry and put in "Dora Mylchreest Quayle, b 1898 IOM", then you get a list which includes 3 entries for her. All of them are "personal", so you have to contact each one in order to find out whether DMQ was a closely related or a peripheral family member.
If you're lucky and one of them is a descendant of one of DMQ's close family, you might find that there's some family knowledge, either written or oral, which might place DMQ in the immediate period after the end of WW1. Say, for example, she'd been working in a military hospital in N Wales....
Or you might find information which would enable you to cross DMQ off your list of possible grandmothers.
Worth a try ?