Agreed that "yay, dead!" is disturbing, and agreed that it's horribly sad to think of her alone when all her family and friends have died. That's what "The Problem of Susan" (which is in the Flights collection I linked to in my post) is about, really... a Susan who grew up alone after all her family died when she was a girl.

However, in the series Susan was the skeptic, and the less cooperative one (after Edmund shaped up), and in Prince Caspian there's a point where she admits that she actually believed Lucy about Aslan and still didn't follow him. I forget what is said about her later.