This is the first X-Wing ever produced by LEGO. I have never taken it apart. With R2-D2 and Luke Skywalker. (Got to tell you, there is a little yellowing on R2, especially on the backside.)
Holy shit! It sounds like you've got a terrible sister!!
As to your other problem, I'd recommend looking into bricklink for any pieces and, as far as I know, used sets. Now, if you can build those sets but not need anything that identifies it as that set, then the prices decreases.