After considering a few of the alternatives, my best guess is that your "Lilydale Younger" is probably one of the clones known collectively in North America as 'Banshee' (disregarding the one or two false "Banshee" that have also cropped up more recently.) There is something very distinctive about these that the rose in your photos shares, in my opinion; the combination of leaflet shape (the way they taper toward a very narrow point near the rachis is one of its calling cards), bud shape and glands, and light pink petal coloration that is difficult to ignore--but the fact that there is not just one clone, and its different appearance under different conditions, makes it unlikely that you might learn anything beyond that general guess. One of the genuine 'Banshee' has also been mistakenly sold in recent times under the name 'Minette' (which belongs to a true Alba that is probably not in cultivation on this continent). If the R. carolina 'Plena' that we grow today is the same as the original, then it is quite a different plant, in spite of a few similarities (flower color and close relationship to species in the R. virginiana-R. carolina complex.) Other than that, 'Banshee' is a rose with origins shrouded in mystery; if you have a clone that actually opens its flowers rather than balling most of the time, then you have a real winner on your hands, because it can be a fantastic rose!