I have to say that while it is hard to fight with her, she did choose quite an adorable nightgown to be so attached to.
Here is the reason she loves it so much: about two weeks ago, I found a video on YouTube of a show that is performed in front of Cinderella's Castle at Disney World. It has all of her favorite characters in it including Mickey, Minnie, Cinderella, Snow White, and Peter Pan. It's full of singing and dancing and it's pretty adorable in my opinion. Here's the link if you are interested. Her eyes light up every time she watches it.
One morning I turned it on for her when she just happened to be in her Tinkerbelle nightgown. She started watching and dancing along with all of the characters. When the Princesses came out to do their song, I twirled her around the room and she loved watching her skirt twirl. She used it to curtsy and spin. It was pretty much the cutest thing I'd ever seen. She now thinks the nightgown is her princess dress and she wants to wear it as much as possible
Every time she watches the video, she asks me to dance and we twirl, spin and sing along. It's so much fun and I had to record it. As hard as it can be to have a strong willed toddler, these moments make it all worth it. The video is long, but it's good I promise! If you watch to the end, you'll hear her say "Bye rella (Cinderella), see soon (see you soon!)"