While we do not have DID or OSDD, we are a tulpa system with trauma. We figured this out after CBT was not working and by finding EMDR therapy effective.
If the end result isn't DID/OSDD, then it could be dysfunctional tulpa-like plurality presenting with other mental health issues. Treatment for those other issues will help them heal. Ultimately, not getting the DID/OSDD label doesn't mean there's something else going on or that your friend's pain is illegitimate. We still find it both helpful and important to go to therapy to talk about system dysfunction when it comes up (edited)