Before we begin to look into your friend’s needs, I want to take a moment to talk about you and your character. You friend is very lucky to have you in her life. I’m not sure what advice I’ll be offering that will be helpful, but I can assure you that your friendship is something that is admirable and a very powerful and dynamic example of your concern for her well-being. That said, there is also a delicate balance between wanting to help and being able to. For your own well-being please remember to take good care of yourself, and that because of the extreme nature and difficulty your friend is having — you may not be able to help her as much as you like.
It sounds like you’ve done your homework in helping to understand more about your friend’s symptoms. Dissociative Identity Disorder (DID) is an identity disorder that needs to be diagnosed by a mental health professional. So the fact that your friend is going to a psychiatrist is good because, in spite of her mother’s reason, she can explain her symptoms and the psychiatrist will be able to follow up from there.
It is called an identity disorder because there is a disruption in the individual’s identity. This can mean that other personalities can come through and “take over” this individual. When this happens there can be profound changes in their emotions, behavior memory, consciousness and senses.
The gap in memory makes everyday event hard or impossible to recall and it make normal continuity with friends and family and daily functioning at work and at school very difficult.
However it should be noted that there can be other causes for these symptoms, and while I agree there seems to be many factors here that point to DID, there is a very real need to have your friend see a mental health professional so these other possibilities can be ruled out.
This brings us to what you can do. You can continue to be a support, offer to go along with her to the psychiatrist’s office if that feels okay and your parents agree. If your friend wants to talk to a school counselor you can offer to support her in that and walk their with her as well.
Your friend sounds like she is going to need a great deal of help because she is coping with a difficult mom and also needs a psychiatric evaluation. As a friend you can help by being a good listener, and assisting her in getting to the people who can figure out what is happening. Beyond this, you have to take care of yourself. Don’t make her your only friend and only concern. That can be very draining for someone 13 years old, and it has the potential of causing you distress. Help her but not at the expense of depleting yourself.