Expansions

I already have one 80 but I am going to start up a new account tonight so my gf can play with me ingame when I'm home. Always funner to scream AGGRO to your tank, that is three feet from you.

Anyways will I have to buy the original game, BC, and Wrath for her to play? Or will buying just wrath be good enough since both our computers already have the full game installed on both of them?