I do believe expecting people to change [random] decisions and actions that do not directly affect a person is a breach of etiquette, but I also know people with broken hearts are sensitive and irrational, and I am empathetic. If the situation was different and she was in the photo, there was trauma of any kind related to the end of the relationship (abuse, death, a nasty break-up, or anything else), and if I knew the circumstances and commented anyway, I'd be at fault.
I am bothered by people who make up rules, do not inform others of those rules, and then get upset if we break the mysterious, unspoken rules. This is skirting that territory to me. I also like this woman and wouldn't want to hurt her. There is probably something else going on with this break-up that she isn't telling me. It was easy for me to just delete my comment.
It's kind of funny because my target was picking up the signal of the other woman in the photo, who seems to be going through something and has grown distant from friends. V's ex interfered with my effort. LOL. Oh well. I will find another way.