Change your approach to her practices, and it will change her attitude towards it. You have turned this into a battle of wills instead of approaching it as a chance for her to master a difficult skill.
1. Stop fighting with her. If she doesn't practice, she doesn't practice. Tell her it is her responsibility to practice before each lesson, and that she will only be holding herself back from learning new/more interesting songs if she doesn't master the skills her teacher is assigning (such as reading music).
2. Stop hovering. Tell her you are not going to sit with her unless she wants you to because it's not helping her, and then give her a chance to rise to the challenge. Last year, I was having this same battle with my oldest son. It was horrible for both of us. We were both angry and frustrated, and it was because I was trying to control how/what he practiced. When I backed off and gave him space, he struggled initially. He would get frustrated and walk away, but eventually, he'd go back to it and master whatever skill/song he had been struggling with. I can't remember the last time I had to tell him to practice because he isn't using it as a way to fight with me or prove himself to me. It makes a big difference.
3. Make it fun/rewarding. I cannot express strongly enough the benefits of well timed bribery/incentives/rewards. Call it what you will. Sometimes kids need a more tangible goal than, "If you practice, you'll be able to read your music." My boys' piano teacher is awesome in her ability to tailor her approach to the needs of her students. She has developed all kinds of incentive programs for her students including candy bars for consistent practice, rewarding them with songs that are exciting/appealing, and in general, makes a huge effort to praise, praise, praise their progress. For one of my boys, the thought of getting a candy bar for practicing x number of times in a row is enough to motivate him. My other is motivated by music that he likes (ex. the Star Wars theme). Find something that works for your daughter and use it to reward her progress.
4. Think outside the box. My sons' piano teacher uses all kinds of techniques to help her students make the most of their lessons. She made flashcards to help my younger son learn to read music, and we used them as a game to help him learn where the notes are. She also made practice hats for them (foam sun visor style hats), each with a different skill written on it. They were supposed to physically change hats when they were focusing on a different skill (counting notes, relaxation, fingering, etc.). She also teaches them to have goal-oriented practices instead of a set amount of time. For instance, she'll have them play through their songs five times during a practice session. If that takes them ten minutes, fine. If it takes 30 minutes, so be it. It takes pressure off the kids while at the same time encouraging them to focus on their trouble spots. The key is to find an approach that encourages the skills without turning them into a battle.
My last bit of advice is to have an honest talk with your daughter. It's possible that she just doesn't like piano or that it isn't what she thought it would be. But it's also possible that she just feels a lot of pressure from you and/or her teacher to be good/better. I had this talk with my oldest last year, and he said he wanted to quit his lessons because it was just too hard. I told him he could quit at the end of the school year if he decided that he really wasn't interested, but in the meantime, I asked him to really give it his best so that he could know at the end of that time that he hadn't just given up because it was difficult. After we had this talk, I backed off and the piano teacher changed things up for both of my boys to make it more enjoyable for them. We have never had another conversation about quitting, and they have both progressed tremendously since that time. I'm not saying they are musical geniuses or will one day become concert pianists, but they are learning a skill, and they're enjoying it in the meantime.