DID? I doubt it. From what I understand (which is admittedly not a lot) people with DID cannot generally summon others within their system. Now I did say generally, there will always be exceptions to rules.

I would, however, say that it would appear that your friend does have something going on. It is not within the realm of normal behavior to go around self summoning Harley Quinn or telling people they are the reincarnation of a fictional character. Unless, of course this friend is the sort of person who does things for the sole purpose of messing with people. It is difficult to say without knowing this person. I have known people who do mess with people for whatever reason. I have also known people who have mental health issues and behave in 'odd' ways as a form of attention seeking because something is wrong and they need help. I have also known people who are, for example, schizophrenic and need their meds tweaked when they start exhibiting delusional thinking.

Short of it, it could be anything.

Amsterdam