Still no luck, i called my nan yesterday and she's put me at ease a little.
She said it's just a ring and although it's sentimental she would much rather i have lost it while wearing and loving it than having it stuck in the back of a cupboard not being seen or used.

She's going through the same at the moment, she had an opal pendant she was given for her 21st set aside for DD1 (as it's her birthstone) and it's gone missing too.. maybe my great nan is playing tricks on us