2002 Expedition Sagging

I have a close friend a few hundered miles away who has a 2002 Expedition. She noticed the rear end sagging a few weeks ago and took it to several places to get it checked out. They told her that she had air bags and that it was messed up causing the sag. Another guy looked at it and told her that she had both airbags and shocks but no springs. I personally haven't looked at it but have never myself seen a rear-end set up where they have both airbags and shocks. I am used to seeing customized rides with helper bags for added load carrying capability or with bags, springs and no shocks. But never have I seen one with no springs and only shocks and air bags. Wouldn't this cause the rear axle to not remain stabilized? I thought they had to have a 4 link suspension in place to remove the springs in the rear. Any and all insight will be greatly appreciated.