If she's hesitant to believe that DID even exists, you're definitely talking to the wrong person! If DID is what you're struggling the most, then someone who doubts its very existence can't help you at all in dealing with it. Very sorry to hear this; invalidation (especially from a therapist) is devastating.

In my opinion, the only person who can tell you whether or not you have this, is you. No therapist can know exactly what we're going through, no matter how much we try to make them understand. They're not in our head (though we sometimes think they are...) and they don't experience our lives for us. All they can do is piece together their professional knowledge with our personal experiences to try to come up with an answer. They can easily be wrong.

Please don't let this get you down. If it would help, get a second opinion. In all areas of medicine and health, a second opinion is never a bad thing.

Take care