I go along with Ian - actual videos of different detectors used on the beach with their settings. I use the Minelabs so have no problem but often talk with new hunters that get quite frustrated going near the water. Usually I can tweak their sensitivity to allow them to hunt but they lose a lot of depth. Some schooling on this might be a big help. Miss Mary uses the Omega but it gets jumpy near the water.
Tell Miss Mary to wear heavier boots.
That should cure the jumping.