What exactly is the younger child jealous of? Does she think the older one gets special attention? Or is it jealousy of the older one's looks or smarts or something of that nature? How Aspie is the older one?
I'm a 37-year old elder sister with Aspergers (self-diagnosed), and once I finally recognized my younger sister's at times being jealous and at times looking up to me, I took steps myself to make our relationship a million times better, so maybe I can offer some advice if I get a little more info.