According to the articles that have been released so far, the reason she invents something in the live action film is so that she has more time for reading. Her "thing" is still reading, it's just that she's now applying her knowledge from books to something practical that benefits her and gives her more time to read. As for the dress, it doesn't look like wearing a corset would have changed anything about the design. The bodice even looks similar to 18th century stays, although the bottom part of the dress clashes terribly with it. But considering what Lily James experienced for her Cinderella corset, I don't blame Emma Watson for not wanting to go that route.