I have a master's degree in music, so I've spent alot of time in the practice room over the years, up to five hours a day at some points.
I think it's normal for children to not enjoy practicing--I hated it until I got to college.
I think the key is to find a way to make practicing intrinsically motivating. She needs to come to enjoy the process of perfecting something. Easier said than done! There is a certain amount of tedium in practicing that can't be avoided. But, I feel the problem for most people, adults included, is that they don't know HOW to practice. Most people practice by simply playing something over and over and over. That IS boring! They haven't learned how to mentally engage, how to use their minds creatively to make practicing both more efficient and more interesting. There are lots of techniques that can add variety to practice, but they are kind of specific to the instrument, so the ones I've used probably wouldn't work (I'm an organist).
I would sit down with your child's teacher and discuss this, asking her about ways to not only practice, but to practice BETTER. I would get on the internet or try to get access to teaching journals or other publications that would have creative ideas to help students and see what you can apply at home. Then, when you are armed with some strategies for your daughter to use, you will probably have to make a commitment to closely supervise her practice for awhile as you help her learn how to make her practice sessions more effective. Help her learn to use her mind so that she can be in control of her own practicing to make it work for her. Depending on how much of a musician you yourself are, you may be able to help her draw out of herself this kind of thinking by being there in person to model to her how to make practice more meaningful.
Motivation is a very complex thing. I took a whole class in graduate school on theories of leaning and motivation in music.
One other thing about practicing is that it's usually so isolating. Does your daughter belong to an orchestra or some other group where she gets to play with other people? Maybe she has a friend who plays the same instrument with whom she could get together and have joint practice sessions, just for some variety. Have her record or videotape herself playing.