I have not gone through surgery yet but I have completed 8 months of intensive outpatient therapy for an eating disorder and it has been really helpful. Your therapist may simply mean that surgery will be more successful if you resolve stress eating in advance. The IOP I attended included DBT therapy and supported eating which were really helpful.
Did your therapist discourage WLS, or did she tell you to work on stress eating prior to surgery? If the former, I'd get another therapist. If the latter, I might still seek out someone who specializes in stress eating. Does your surgery clinic also have a therapist and nutritionist? That might be the way to go.
PCOS does wreak havoc, no doubt about it. But from what I am told, surgery doesn't cure stress eating. But there are indeed therapies and therapists who can help you with this if you need it.