why is it "is" rather than "heeft" following zij?
Some verbs use "zijn" (to be) as an auxiliary in the present perfect. See here for more information.
Is there in Dutch the same difference between she went and she's gone when you say zij ging and Zij is gegaan
Does Dutch also have the difference between "she has gone" and "she has been "?
"She has gone" = Ze is gegaan; "She has been" = Ze is geweest, I think.
Thanks for the reply. So, as in English :gone> meaning that you haven't returned, and been> that you are back from X place?
Pretty much so, yes.