Clearly you believe you have alters/parts, as you posted something recently about working with a younger part. And I also think that your therapist believes you have them, or she wouldn't say that she agreed with the diagnosis.

It's not your therapist's job to believe you or not, but to work with what you believe. It's not her job to tell you what to do with your life, or what to watch on TV or what music to listen to. It might be her job to help you discover any of these things that are interesting or important to you.

And the answers to your specific questions are really unknowable, so that is a "straight answer."