Erin, Excuse the crude drawings (doing this on my phone).

I was thinking something like this...

Raise the height of you curtain rod and put extra curtains - when curtains are pulled to allow light in they can be pulled behind the headboard. This will give the illusion of a full window. Put a light piece of art like a branch or similar which will fill the space when the curtains are closed. I would keep the fabric light sheers and maybe a lighter subtle pattern black out (if you require) on top.

Depending on what your budget is... you can put barn doors in a simple design which would fill that wall nicely but not overwhelm. You could also do them in a mirror, but this makes it more rustic and industrial. If you're handy you can make your own barn doors :)

I would put a full height freestanding mirror in the corner - these can come in a variety of finishes. Depending on how much storage you need.. You can put a small seating area next to the mirror (2 club chairs and a small side table) or a longer and lower dresser to fill that wall a little better.

I hope this helps!