Hi,
I have trained many cockers in my time, made one up to a Field Trial Champion, my advice would be to contact the
professional trainer in the first instance to see if he has experienced the same and see what he has to say first place
If the dog was mine I would hunt her in light rushes first if she makes a sound say to her quiet or no in a stern voice let her sit to absorb that she has done wrong and cast her off in a different direction, hunt her close to you and repeat over and over. Hope this helps.