My girlfriend has been feeding her Dachshund chocolate for 7 years.

Ever heard the saying "Living on borrowed time?" Well, I think that about explains it. One day he just won't recover from the wheezing and gasping. Most likely the only reason he is still alive is that he is not always around her. I can not believe that reasonable pet owners would allow this to continue. You say her family does not know - tell them !! I would.