the novel has not been published yet even in the UK, so I am not sure about its definite name.
I believe it is a Black Country word from approx. 90 years ago (period after the WW I) but I haven´t found it on the Internet BC glossary either.
I can only provide a part of the review:
The novel, set in 1930s England in a landlocked industrial town still haunted by the Great War, focuses on the motherless thirteen-year-old Ruby.
The book has drawn comparisons to Thomas Hardyʼs Wessex novels.
I don't know if it's useful, but I made a search for "mourning" combined with "textiles", and, among other things, I found these sources:
Source 1 (Art of Mourning) and Source 2 (Teaching History with Textiles). Both show that special textiles were made for mourning, source 1 explaining the development of clothes in the course of the centuries. And linen as a material seems to have played an important role here. I find especially the second source quite instructive because it shows that not only clothes, but also other textile objects were created for mourning purposes alone.
Excerpt from the text (Source 2): "Mourning handkerchiefs (Figure 8), as well as mourning crepe, mourning veils, mourning clothing, and other mourning- related artifacts, can be found in many museum collections. These simple handkerchiefs consist of a white linen or cotton center with a one-inch black border. Examples of hand-stitched and printed black borders can be found."
Maybe that in the area of Great Britain that the novel is set in, linen played the major role. Just my guess.. That's what I can contribute right now