I think you're going to have to be a little more directive to get what you want. You don't have to lie to your T in order to talk about something else. You can just say, "I've been thinking about it, and there's something important I want to talk about today that isn't my eating disorder..." It's your therapy; she should be open to talking about what you want to talk about.

Similarly, the only way to get more frequent sessions is to ask if that's a possibility. She can't read your mind, so she can't help if she doesn't know what you need. Does she allow email contact? That might be an easier way to bring this up if in person is too scary.