That does sound really hard - responding to scowling in a sunny way. One thought off the top of my head, is to figure out another way to respond that feels both loving and authentic. Think of your own code word - something like, poignant, observant, stillness - to remind yourself that maybe it doesn't have to be sunny?

Ask dc what the scowl means - teach her to explain it in more complex ways over time (more nuanced feeling words, more backstory to the scowl). Eventually, begin to talk to her about how you feel when you see the scowl. Even something simple like, when I see that scowl I'm not sure what it means and I don't know what to do. Then I clam up or start to feel frustrated ...

Since she's not much of a talker that way for the time being, there's also an exercise I've done with kids called The Weather Inside. So what's the weather when the scowl is there? She can draw or just describe it. What's the weather when she's smiling? (You can ask that one later ...).

Anyway, just some ideas off the top of my head. She sounds like a great kid.

RachelD

see the impression they are leaving.  I do it through humor.  Sometimes it works, and sometimes it doesn't.  When it doesn't work and I'm really not in the mood to play nice, I do turn it back on them a little.  Nothing wrong with letting some one have a dose of their own medicine every now and then.  Ofcourse, being a mother, I have to point out that this was my deliberate intention.  

My older son, who is a bit scowl-y, usually chooses people to associate with who are very different.  I think that says something.  I'm very glad that his girlfriend is a lot like the females in our family.  Its as if he's trying to somehow make up for what he considers less positive features about him self.  I think part of him recognizes that this really isn't how he wants to be.  And a little reinforcement from sources outside the family isn't a bad thing.