Cora is looking very beautiful, thank you Mary Jane Watson, but very uncomfortable. This isn't really a position she's used to being in, or has had the opportunity to be in, and as a result she doesn't really know how to handle this.

As a result she's taken to hanging out in the area by the food, trying not to draw too much attention to herself. Every so often her hand wanders up to play with the strap of her dress, or with the way her hair sits against the back of her neck and then drops immediately once she realizes what she's doing. She feels ridiculous and out of place, but there's not really much she can do about that.

Basically, you should distract her. It'd probably be the only way to get her to relax.

Alternatively, you can get her drunk, but that might take some doing unless you're someone she trusts.