I can empathise with the situation - I too prefer to work at something in my own time and find 'performing' for others stressful.
Its perfectly possible as a parent to do both of the following:
Firstly, acknowledging that she feels that she has been treated unfairly by her peers and teacher. She feels that she has done most of the first stage of the task and resents being forced to do most of the second stage. Genuinely acknowledging the unfairness of this is honest and respects her perspective. Its also important to acknowledge that performing in front of others can be difficult and stressful. Again this validates her feelings.
Secondly, providing a different perspective on the situation. Her teacher may well be aware that she is the most able member of her group. Insisting that she does take the lead role gives your daughter the most opportunity to display her abilities and earn the topmost marks. If it is an area that her self-confidence is lacking in then it gives her a valuable opportunity to strengthen herself in this area. If the teacher has not given her adequate support to do well in this role, then its something you and your DD can work together on over the weekend (learning the part, giving her a chance to master speaking in front of others).
I don't approve of chucking people who are underconfident in at the deep end and hoping they'll figure out how to swim on their own - so can understand why your daughter is uncomfortable. Ideally, she would have been able to work at this 'speaking in public' thing at her own pace, with proper guidence. But it is the situation she is faced with now and you as her parent can give her some of the support and encouragement she requires.
Part of this is helping her understand that it's ok if this is something that doesn't come easily to her, and that she doesn't excel in first time around. She can try her best and improve at these skills over time.
I was an intelligent and reasonably able student at school. But there were things I struggled with - revising, organising my time, confidence and performing in front of others. Sometimes, being good at other stuff makes it hard for teachers to see that you need support in these areas, or makes it difficult to ask for help.
I've taken a more generous explanation for the teacher's seemingly unfair actions than some others on this thread. I think it is good to assume people are generally trying to do the right thing. However, if it is the case that she isn't a good teacher and is using your daughter as a TA, then there is a way of framing this too:
At school, some of my able friends had a maths teacher that they reguarly complained about. He reportedly couldn't manage the more distruptive pupils and the class spent much of its time in a disarray. My friends (quiet and studious types :) ) felt this impacted on their learning - and indeed they were right. However, whilst some of them were content to blame this teacher for less than expected performance, others made sure they worked hard with their textbooks/each other/parents outside of class to achieve what they were capable of despite their teacher's poor class management and their classmates' rudeness.
My point is that they took responsibility for their own learning, and realised it was they, and not their teacher/classmates who would ultimately decide their grades. Obviously it would have been better for them all to have a better classroom environment, but they worked around this less than ideal situation and still got top marks. Meanwhile those moaning about the teacher/class who expected to be passive recipients of 'an education' probably did less well than they would have liked and were capable of.
So your DD, whilst I completely empathise with her emotional reaction to her treatment, can either walk out of class/stay off and let it affect her grades and blame the teacher and her 'team mates' for the result. Or she can acknowledge how angry and upset she is but then do her best to prepare for and give the presentation to make sure she gets the marks she deserves.
It wouldn't be unreasonable for you/her to make sure the teacher is aware of how much of the work she did on the writing side of things (though I'd keep personal opinions about the other students out of it). But I do think she would be cutting off her nose to spite her face if she walked out/otherwise refused to participate. Of course, she can choose to do this, but I think you should make sure that she understands that her school are unlikely to take away the message from her actions that she would like them to.
I'm choosing to ignore the slights you've made on her classmates. I think they are unpleasant and unnecessary. I do understand though that she may feel intimidated by her peers, and annoyed at them for the way they have treated her.
Sorry for the long post. Basically, I think you should validate how she feels about the situation but encourage her to proceed to the best of her abilities in spite of the unfairness (percieved or real) for her own benefit. I also wonder how much of this is to do with her own anxiety about performing, and that she should be helped to feel more confident about this over the weekend whilst reminding her that it is a skill which she can improve at and that she doesn't have to be perfect at everything first time (she could be putting a lot of pressure on herself, and she's probably anxious about the reaction of those watching if she feels unpopular).
But yes, performing in front of others is difficult. I wouldn't want to be in her shoes. Good luck.