There is often quite a few memories, even from really traumatised childhoods, where things were sunshine and lollipops, or at least, the sunshine facade that we put on for the outside world. Kids have a very innocent understanding of the world, and emotions. Put a kid in front of a sad movie, they don't just cry, they feel sad with their entire being. And when they're greedily unwrapping a gift, or swinging they're way across the jungle gym, they're happy with their entire being and the whole world around them they interpret as a happy utopian place, even for a brief moment.
For many people, connecting with their inner happy (naive, curious, innocent, etc) child is a huge part of the healing process. They're in there somewhere: the child who wanted to believe that the whole world was a happy, safe place. For many, that child didn't get a chance to be out there in the world, but they still exist somewhere inside us, and we sometimes experience them when we play with a puppy, or want to jump in a puddle, or indulge in an icecream. Nurturing that part of us is a way to connect with our joy, which is just as important as confronting all the negative emotions that form part of trauma recovery.
For DID, this happy inner child, and the trauma inner child, may exist as 2 seperate alters. But otherwise, even without DID, knowing she's in there? An awesome opportunity to experience joy.