If she is using the new DSM....well, it's been rejected by many including the National Institute of Mental Health...and DID is real, as is was when called MPD, or...whatever name you choose.
What does she say is a "real" diagnosis? I can understand how telling you something is not real would cause conflict, it is invalidating. Diagnoses are really just ways to describe a particular grouping of symptoms that add up to something that we can discuss, knowing the other person understands what we are talking about.