Wow, have never been there myself, but I would think telling her therapy has been successful and you're ready to move on would not hurt any feelings! I'm sure she'll be thrilled. I always thought at this point in treatment that's what you did, then maybe had a goodbye session or two, spaced far apart to wrap up things. But really once you tell her you feel like you're ready to be done I'm sure she'll know where to take it from there.