I would contact the teacher. Let the teacher know what is going on, so she can help to make sure that your daughter is being included and treated fairly.
Perhaps she can even say something to the class about being nice to each other and helping each other out without making it obvious that it is aimed at these girls. Or she can also pull the girls aside privately and ask them what is going on and if they can work on being friends again.
Do you know any of the girls mothers? Maybe you can call them and let them know.
Sometimes a group of girls can be harsh when around the 'big shot' one, but if one girl that was the closest friend was invited over for a playdate or something, it might help break that up.
In the meantime, encourage your daughter to still be nice and friendly and that over time, things will blow over. And if they don't then that is okay too, because she will one day be able to make close friends of her own who won't treat her badly.