Little Kitty, I was thinking also of this costume. If I remember correctly there are 2 different costumes she has? One where she is walking through the house in the real world, and another dress when Josh is in the memory with Parker.
I think the dress from the memory might be easily replicated without a pattern, which is the one I planned on. The other one seems a bit complicated- if you google victorian or 40's patterns you might find something close.