I don't think I can help. I have two mature peahens (7-8 years old) who hatched peachicks last year and now I can barely tell the mothers apart from the yearling hens.
I see your hen has spurs and someone else mentioned spurs growing on older hens. However, out of my 7 peahens in total, I have two who have spurs and only one of them is a mature hen. The other is one of the yearlings. So I thought the spurs might just be a hereditary trait rather than a sign of age but I am no expert on the matter.
I do have a question for you. I see from your posts and photographs that you live in a beautiful spot surrounded by forest and that your peafowl are out and about at least some of the time. How do you know the peahen isn't laying eggs in the forest or somewhere else secretly? And likewise for them mating. Maybe you're missing it? It is very quick and is over in seconds when it happens.
You say your peacock doesn't even try it on with the hen but does he not display at all? In my experience, the peacocks spend the entire day during the breeding season either displaying or preening, with an occasional short rest and lookout on a roost. The actual mating is a rare sight, although I hear it more than I see it now that I know what it sounds like. The peacock will make a distinctive sound. Maybe you can find it on youtube or something so that you can know what to listen out for.