Children who have a bit of anxiety in their genes can suddenly have an episode of anxiety after being "triggered." Your son's playful ghost hoax was a bit much for this sensitive little girl; she is experiencing something like a post-traumatic-stress reaction. Fortunately, these things are usually easily cured with one or two sessions of specialized therapy. The type of therapy that will probably be quickest and easiest is Energy Psychology. You can visit www.schoolmademucheasier.com to learn how this technique is used for many childhood issues. You can see examples of one form of Energy Psychology (EFT) on www.youtube.com.  There are also books on the subject. However, the fastest treatment may come from an experienced professional practitioner of Energy Psychology. If you go to www.emofree.com you should be able to find an international list of practitioners. Alternatively, you can try Bach Flower Therapy for your daughter. You can learn about this at www.bachflower.com or www.bachcentre.com. The remedies Star of Bethlehem, mimulus, aspen and rock rose (mixed together in one bottle) will likely be very helpful and may just "melt" her fear away within some days (or a couple of weeks).  If neither of these approaches appeals to you, you can just take your daughter to a child therapist for regular treatment. However, I do recommend that you do SOMETHING. If she hasn't been sleeping for a month, she is suffering intensely with no sign of healing on the horizon. She needs help.    All the best,  Sarah Chana