MrsJamJam has it right: the first thing to do is to speak to the teacher. I can remember people like this at my primary school - and believe me that was a long time ago! There is always, always, one child in a group who will behave like if not checked.
Agree with the above, but would also add that it would be worth making an appointment for a proper talk with her teacher (don't just grab a few minutes at the classroom door). Since the main problem is in school, any good teacher will have an understanding of the dynamics of the friendships going on in her class and will be able to offer ideas of the strategy to follow.
This is a very tricky issue. When I was about the same age as your daughter, I found myself in a very similar situation. I recall that my mother must have guessed that I needed an escape route. She, unbeknown to me, invited three pleasant friends to tea. The three pleasant friends had pleasant children. As mothers gossiped and drank tea, we youngsters had some fun together. In turn, the pleasant children invited me to their homes...and one day, 'manipulative friend' was no longer an issue, as I had outgrown her...
(This is another Ask a gran question sent in by readers of the Radio Times.)
My 8 year old daughter seems to be in permanent thrall to a quite manipulative, powerful ‘friend’ in her class. She is frequently in tears by the end of the day. I am trying to get her to stop being a victim and to walk away and play with other girls, but she is like a moth to the flame. How can I help her?