Thank you for trusting JustAnswer with your important question.
Yes it is possible for there to be alters that the main alters do not know about. They can either be alters that split from the little girl alter, and now seem to live inside her; or they can be cut off from the other two alters you've talk to through dissociative barriers. It could be that the rest of the system decided the body would be safer and more functional if those two alters didn't know about the others and the information/memories/emotions they may be holding.
I'm not sure what you've read on the subject, so please feel free to tell me what some of the books are you've already got. I can help point you in the direction of a few more.
But I've talked with many systems that had strong divisions. Some systems are set up in levels like a house, there they talk about alters being in different areas of awareness based on how high or low they are. Some systems talk about the division being more of a good versus evil, light versus dark side, or safe versus unsafe type terminology. Many times the alters that hold most of the traumatic abuse, and the most volatile emotions, are the ones lumped into the less desirable place/group.
I've also seen systems that appear to integrate online to then find the next layer of alters. In that case it's usually reaching a certain level of stability and mental health that allows the internal self helpers to decide that the alters most commonly out are now ready to deal with more information/trauma history/alters. It's a safety mechanism to try to keep from overwhelming or disintegrating/splitting the newly combined alters. It can also be a safety measure to try to prevent overwhelming the counselor and other supportive people whom they might fear would leave if they "knew everything at once."
The biggest thing you can do for her right now is to reassure her that you're going to be part of her treatment team as long as possible, and that you will help her find more treatment team members if needed. Some DID clients have so many issues that they really do benefit from having more than one therapist to work on separate issues. Especially when one therapist may need to work on the DID and trauma, while the other may need to stay focused on one particular issues like an eating disorder or substance abuse issue, or another major life skill focus.
The main two need to know that the little girl believes there are more alters, and they need to be reassured that their internal landscape and system was created to keep the body and everyone inside safe. No matter how chaotic it might feel for them to face that there might be "others", they need to remember they can survive the process of meeting, hearing/knowing, and merging with those alters too. The journey to recovery never lets us see the entire road at one time. We take each twist and turn in the road with limited information and an obstructed view... but we keep moving forward through the peaks and valleys.
Encourage the little girl to create a system map with you. What does the internal "family tree" look like? What does the internal landscape look like? Are there houses or other buildings inside? Is she aware of internal self helpers, historians, or other care takers inside? These alters often seem to be the older (as in created early on in the DID process), and are invaluable in the recovery process. They also tend to be the ones with the most knowledge about what all is really going on inside.
You also can start trying to listen to see if these others appear to be fully developed alters, or are they more one-dimensional and temporary, what would be called fragments. Fragments can seem like alters to other insiders, but they are easier to integrate because they don't have as much experience being autonomous as more developed alters.
You may want to contact other professionals in your area who have more experience treating DID for a consult. Sidran.org and ISST-D.org both offer directories of professionals who work with complex trauma, dissociation, and DID. Both sites usually also offer education, books, and treatment guidelines to help professionals learn about treating DID and related issues.
When using tools like hypnosis or EMDR, it's always critical to get a signed informed consent form from your client. They need to understand the psychological risks of these tools, and that these risks are higher for DID clients. They also need to understand that what they remember while using these tools is often considered "tainted" if they intend to pursue legal action based upon the memory/trauma work. Not many are worried by these risks, but it's still legally and ethically wise for you to get this type of information in a written form they can sign.
Selah, Thank you so much, you gave me excellent information. The books I just ordered are "Clinical Perspectives on MPD", Kluft; "Treating DID:Power of Collective Heart", Krakauer; and "DID Sourcebook", Haddock; I also thought about getting "Trauma Model Therapy" by Colin Ross. I live in Dallas so I can also go to the Ross Institute for help. Any other suggestions for reading material or comments on the Ross institute. I see you are offline now so I can wait or have another person answer.