Interesting, I haven't read "Agnes Grey," but it could just be the rather general Gothic atmosphere that seems familiar. Although the situation you describe does sound like it has some specific similarities to DS too. Later in the storyline, DS definitely borrows from "The Turn of the Screw", with the troublesome children, ghosts, and the governess.
I don't remember all the "Jane Eyre" parallels other than the mad wife hidden away who sets fire to something. If I'm remembering that correctly, it's definitely straight out of "Jane Eyre."
