In my mind this is what I think you should do, but in reality, probably not.
Next time Sis has a birthday, if I were you, I would be all over her every time she opened a present. Take it and start opening it. Oooh and aaah over it. Try it on, or try it out. When sis complains and raises a ruckus, because she will, "Innocently look at her and say, "Oh, I'm sorry. I thought this was your norm. You see, every time younger daughter has her birthday, you let older daughter do what I just did."
Hopefully, the light bulb would go off in sister's head.
But, alas, probably not.