Sidna Nourse was a commercial portrait and landscape photographer in Picton Ontario into the late 1940s. I may be able to find her dates in business more definitively in a couple of weeks, when I think that I can gain access to a reference on commercial photographers in Ontario. If so, I'll pass them on.
Coincidentally, she and her husband lived on Johnson Street in Picton, near the home of Reginald Nourse, a Picton lawyer, but no relation, as far as I can determine. Reginald Nourse was my spouse's grandfather, and we have several hand-tinted family photographs signed by Sidna Nourse.
While not genealogical, this may help put Sidna Nourse in social context.