I found a link of an interview with R.O. And lost it before bookmarking. The interviewer asked Robin about the romance in the novel between Mary and Degas and it appears Robin took liberty and made it up. She admits there was NO source that could actually confirm anything other than a mutual admiration each other had for their shared artistic skills, and friendship. So, as for the letters, although I was so looking forward to Mary disclosing their contents in this book, it appears my curiosity is squelched. Imagine my disappointment reading before the end of the story the letters were destroyed. I don't read ahead or search for answers dealing with endings due to finding out too much before I care to.
Considering our author has chosen to intimate there was more of a romance than actuality, from here I will read this story more as "fictional history." The paintings are factual, but without diaries, journals, letters or their personal confirmations, everything else is other's opinions, or assumptions, or the author's imagination to make the story romantic. Which does not lessen the quality of the story, it just puts things into perspective for the reader. So when I read Degas was away writing to Mary inventing an intimacy, now it makes sense to me why the author wrote this.
Ciao for now~
P.s. I will continue to search to find the link to the interview with R.O.