When the counselors allow her son to drown she goes ballistic, hunting down the counselors with no regard for who was actually responsible. The film would recreate each murder from the original, but show Mrs. Voorhees performing the killings.
The film would end exactly like the original with the death of Mrs. Voorhees and the reemergence of Jason.
The trick would be to keep it scary, even though the killer is no longer a mysterious figure. I suppose you could always focus on the tragic side of the story, rather than the frightening.
Who's with me on this?