wait, why wouldn't it be ok to wear a dress at the 100 con?

And yeah, if it's a relaxed group, you're probably fine doing a non-anime cosplay! Nice that her look seems pretty easy to put together (always nice when you can either go shopping in your own closet or find most stuff at a thrift store!). Also, you might be surprised - if you put in effort on a cosplay, at least at DragonCon, you would probably get lots of compliments and potentially people wanting to take a pic with you!