Update (May 2017)
The shop in question appears at the very beginning of this precious bit of film footage:
Returning to our Kinderton Street shop, you can just make out that the window display was in the traditional style with canned fruit and toilet rolls in little pyramids. The child on the extreme right will be in her mid to late forties now (I think it's a little girl, but it's a bit hard to tell with that 1970s 'page-boy' hairstyle)
Incidentally there's a good view of this shop in 'Middlewich' by Brian Curzon and Paul Hurley ('Images of England', Tempus Publishing 2005) but it is mysteriously and unaccountably labelled as 'Leadsmithy Street'.
Mary was the wife of Clarence Costello, councillor and one-time chairman of the UDC. She only died in recent years in her 90s.