I am reading back over the letters - now with a different view to them.
She was not the best with her handwriting.

This is an example of what she wrote
"Well my mother was a daughter (one of them) of my grandfather"
Really!!

Sorry, being a little synical here, anyway have found a couple of new things that might be of more use now.
"I am now 76 years old yesterday" this letter is dated June 12th 1983.
So, by my calculations she was born on the 11th june 1907.
I suppose she could have been registered in the Sept. qtr and be the Ivy Kathleen Matthews.
Also in another letter dated 1983, she states that only her and one brother left - perhaps this is Cyril she is referring to.
I will keep looking to see what else might help.
Margaret