It sounds to me like one of the littles panicked because of what she heard, or what she thinks she will hear or have to talk about. Making sure that everyone knows they don't have to share anything until they decide to, or need to, might help calm the situation I think.

I do caution you about support groups, unless it is strictly for those with DID, most will not tolerate it well, unfortunately. Plus, from what I hear, often parts of you might not tolerate other ppl's parts and begin acting out. It's a tough call, imo.