She has been planning this whole escape for the length of the entire chapter. We're shown she gathers bits of food so she can last a couple of days outside, gets a lamp so she can see, is learning the timing of the guard change, trying to learn the layout of the mansion, and so on. And then she throws all that away and risks having her freedom curtailed by trying to escape in the middle of a party when loads of people are around? The whole buildup of the chapter was wasted in an impulse.