I remember what I suspect to have been the same shop premises right on that corner, but a little later around '64/5/6 and by then a Gentleman's Outfitter from where I bought some trousers that I noticed on a display model in the window one lunchtime. They turned out to be too long, but I was promised that they would be altered for me by the end of the afternoon. I worked in an office further back up Colmore Row, and when I picked them up they were ready and fitted perfectly!
I know this doesn't directly address your query, but my imagination came up with the thought that for one reason or another perhaps the shop might have remained in the same family but moved over to a Men's shop a little time after, in the hands of another family member who was the man who measured/served me.
Although I haven't even thought about that shop at all in the sixty-ish years since then, I think that the name was Rayner or Rayners - too close to your 'Raymar' to be a coincidence I suspect - on a cream name-board in a brown, script-like style of lettering.
And one final thought, though this may be completely fanciful! I'm not sure now, but I formed the impression at the time - maybe from something that was said or on a notice - that alterations were dealt with on the premises, and so maybe it was a service that had been offered for ladies' gowns earlier also in a back room or basement or wherever. If so and it was your Grandmother who was the skilled seamstress, maybe it was she who did such perfect work on my new trousers!
I really hope that this has some relevance for you and maybe adds a little something to your wife's awareness of her Grandmother, and good luck tracking other things down!