I think a nice built-in storage would be more valuable than the cute sitting area since she can always sit on her bed or in a chair.

I like the built-in storage, but wouldn't it be nice to have shelves for storage inside so you can close it and hide any clutter?

I agree with built in storage. I would remove the doors and have drawers in the bottom area with shelves above. You might look into kitchen or vanity base cabinets with drawers with full extension glides to optimize the drawer space. If you pull the upper shelves forward with 9" or 12" shelves you would have a 12 inch or larger space behind - it might be fun to have these shelves swing out with hidden storage behind. Another option would be to push the shelves to the back and have about 12" counter before the 12" deep shelves start. Have a shelf that slides or opens in this space to make a desk surface. With the space between the closets as part of

the closet space there should still be about a 6 ft. rail closet for clothing.

I would hire a closet organizer to make use of what you have. In 10 years your daughter is going to need the space and if you sell, a buyer is going to think you lost your mind in getting rid of closet space. Have you ever heard a buyer complain there is TOO MUCH closet space? You are going to ruin the resale value of your home by over customization.

You could put a duchess similar to what's in pic, for storage with small ottoman, hang a mirror. Don't attach duchess so its permanent and on resale it can be converted back to a closet or daughter needs it as extra closet later on. In the meantime you have extra storage a desk for school work, which I think personally is a great idea, but an easy option to be able to convert back to whatever