Trying to locate my mother's half sister, any help

[MerseyMan]

In a nutshell my grandad (John Grant Payne) left my grandmother and her children in 1949 when he was based in Liverpool after the war. From his army records my grandad was based at a coastal battery in Edinburgh between 1950 - 1955. After I found my grandad had emigrated to the US in about 1955 I chased down his foster daughter in the US and she told my mother last year he had a child out of wedlock when he must have been based in Edinburgh between 1950 - 1955. My grandad came back over to Scotland to see his daughter in 1962 with with his foster daughter from the US. The foster daughter from the US told my mother her name was ******** and was about the same age as she was (born 1951). She said ******** mother was called ***** .
John Grant Payne my grandad was believed to be living at 6 or 8 Springfield street, Leith, Edinburgh between 1952-1955. I had back the voters roll's for that street from Edinburgh but his name is not mentioned, nor is his daughter or her mother.
I do believe his daughter out of wedlock was born in Edinburgh between 1951 and 1955.

Does anyone know that person, I attach a photo that I captured off cinefilm that I recieved from my grandad's foster daughter in the US. My grandad's daughter (my mother's half sister) is in the bottom right of the picture dressed in red, does anybody recognise this girl, it would mean so much to my mother and uncle.

Short of sticking this picture up around Edinburgh this is the next best thing to get the picture seen and maybe passed around.
I have e-mailed a few Edinburgh sources but have had not much luck, I'm hoping some forums members may know something.

One kind person has looked the birth records for the exact name of the girl (4 exact first name matches born in Leith Edinburgh between 1951-4 but the parents don't match) so I am assuming it could be one of the remaining 49 exact first name matches born in the Edinburgh area between 1951-4.

Anyway I include the photo just in the off chance anyone with contacts may be able to recognise the girl in the bottom right.
I have not put in the first names of the daughter of mother to abide with potentially living person rules that the forum has