Speaking as a parent, a doctor, and an arbitrator at the table of workplace conflicts of many types, my opinion is that many kinds of problems can be solved by figuring out how to express the emotional impact of what's going on without letting the emotional impact dictate the mode of expression.
You have eloquently stated here how frustrated you are, and I can sense that for you, this isn't just about guitar, but about a young person missing an opportunity to use the guitar as a motivator for developing discipline in an enjoyable manner. I totally get that. Does she?
I apologize if you've done this already, but what I would do if this were my daughter (and if you throw in a piano, and some other variables... it is...) is to have a sit down and a heart to heart.
"Honey, this is hard for me because I'm not just your guitar teacher, I'm also your dad and I'm not going to be able to separate these two roles. I'm not just trying to share my love of this instrument and it's music, but I'm also trying to let it be a doorway into a world of more adult rewards. Adults learn to feel best about the most hard won accomplishments, and the rewards are enjoyed even more BECAUSE they take a long time to earn. Learning guitar is a wonderful example of this kind of accomplishment, and I believe that as you learn not only guitar, but how to enjoy the rewards of investing yourself long term, you'll be able to use that same skill in many other parts of your life. I know you'd eventually find this kind of thing true for yourself, but I would love to be able to share this experience with you using the guitar. However, if it's too strange to be my daughter AND my student, I'd totally understand, and if you think you'd learn better with another teacher, I wouldn't be insulted. I love you and I'll still enjoy watching you learn and grow!"
Again... sorry if I'm picking at the already-picked-over areas. It's just really easy to forget to say what you feel, and instead just let how you feel change the way that you say what you think... if that makes sense.
"If I have seen further it is by standing on the shoulders of giants." -Sir Isaac Newton
Armin Hanika 56PF