Hello. Sorry to be annoying, but I was always taught that if someone says that you haven't explained something, or haven't done it clearly, then by definition you haven't. If your reader doesn't understand it, then its not clear. Has she critised the thing that you didn't write maybe because she thought what you did write had that meaning?
I used to get really frustrated by this, but its true. Still, have a good ol' vent!
B.x