Who visited Porters Photographic Gallery in Perth in the 1870s?

I'd dearly love the carte below to be a wonderful clue to the mystery family of Amelia Millar - so I am posting this in the probably vain hope that someone  will recognise it from their family album and say that's xyz and get in touch.

It was found in the effects of my great aunt Nellie FLETCHER, aka Elizabeth Helen Sinton HENDERSON (1885-1981) and it is past time I published it in the hope of an identification.

 

I appear to be looking for a woman aged ??  in about the 1870s, presumably with two children aged about ?? and ??, within cooee of County Place, Perth, Scotland. Possibly widowed or with a camera shy husband?

A quick web search brought up the helpful page Scottish Photographers – 19th century

and showed that the Mr Porter in County Place Perth on the reverse of the carte was rather likely to be this chap:

Porter, James – County Place, Perth -1868/69-1878- and also George St. Perth by 1878

which dates seem likely to fit with the clothes of this unidentified woman with two children.

Add in that James Henderson and Amelia Millar, who are presumed to be the recipients of this carte, emigrated from Scotland to New Zealand, with those of their immediate family still remaining in Scotland, in 1874.

James and Amelia married in 1836 in Stirling but  had moved to Forth, Lanarkshire about 1840.

One son, Archibald, stayed in Scotland but was over in Carnwath, Lanarkshire, the rest emigrated between the early 1860s through to 1874.

James' father Archibald was a blacksmith at the Bridge of Allan and his wife Margaret McEwan's family, were long resident on/around the Kincardine Moss, Perthshire

Amelia's parents are - still - the subject of an onging brickwall search, but likely to be Millar and Chrystal families from around Kippen, Stirlingshire.

Where were James' siblings around this time?
Only William and John of his siblings are documented as staying in the area.

William at the Bridge of Allan, John in Tillicoultry, Clackmannshire.
The rest settled and had their families in Fife and Lanarkshire.

William is presumed to have died late 1840s to 1851, and his children are all accounted for in Australia well before this date, apart from the eldest Isabella, whose fate is still unknown.

John  had also moved to Lanarkshire from Tillicoultry about 1850, where all the children are accounted for in Ontario well before this time apart from Helen, whose fate is as yet unknown beyond the 1851 census in Cadder.

Love to hear from anyone with any answers or suggestions as to who this family are.