Golding's novel was written in reaction to R. M. Ballatyne's The Coral Island in which a group of British boys defeat savages on an island and maintain their civilized ways. To populate his island with girls would throw off the comparisons of his novel, of course.
However, as a theoretical question, the use of all girls would not change the essential theme that civilization merely conditions people to control their innately cruel and jealous nature.
I agree that Lord of the Flies is a picture of human nature which is unchecked by laws or societal restrictions. The result is, of course, violence; and it seems to me the result would have to be the same. There's no way of knowing for sure, of course, but I tend to think an island of girls would have lasted a little longer but eventually ended in exactly the same spot. Girls do, indeed, play dirty and mean; however, they can also keep the facade of friendship going for a long time. They know how to wear the masks, and I think that's the only thing which would slow down the pace of the violence. Interesting to think about, though, isn't it?
This would be a wonderful question for a discussion - you might want to move it into a discussion to gain a number of different reflections and responses. Well, in answering this question I am very wary of responding according to gender stereotypes. If I wasn't so cautious I might respond by saying that if it were girls instead of boys, the violence would be less physical and more psychological and emotional - as girls seem to be a lot better at these forms of violence and torture than boys. However, I do not necessarily think that the overall meaning and theme of the story would be altered. The children (of either gender) would gradually descend into lawlessness and chaos, with the resulting violence of whatever form accompanying this state. Golding's point isn't bound by gender - it is a universal lesson that seriously questions the savagery within all of humanity - not just boys.
I don't know that there is any way to know this for sure because society conditions the actions of girls so much.
My personal opinion is that there would be just as much conflict as there is in the book the way it is written. Having been, for example, the coach of girls' sports teams, I can attest that girls are not immune from coming into conflict with one another.
I would guess that the conflict might not become as violent because girls do not seem to be as violent as boys. However, it is extraordinarily hard to assert this because all girls I (or anyone) have met have been conditioned by their society. In our society, girls seem to be conditioned away from violence.
So if I had to guess, I would say there will be lots of conflict but perhaps less actual violence.
The author's point of the entire book is to demonstrate how human nature is to resort to savagery when conveniences of civilization are removed. Furthermore, I believe he intended to show that the savage beast within us all takes just a few alterations to find. Given that interpretation if authorship remained the same, I think girls or a mixed group would experience similar violent tendencies.
If it were up to me to maintain my understanding of human nature specifically with girls, I think the survival skills would have taken much more time to achieve. I think they would not have worked together as well as the boys to achieve as much as the boys. Girls may have resorted to savagery quicker because girls are mean to each other. Have you ever seen a chick fight? On the other hand, if they were all getting along it might have taken more time to achieve goals, but they would have gone further than the boys in reaching goals. This is because girls multi-task and stick to something until completion.
Human nature stays the same for everyone, no matter the gender, so the ending of the novel and the point behind it would remain unchanged. There still would have been disagreements, but they wouldn't have been so physical, more like gossiping and snide remarks.
It's unlikely that girls would take pleasure in hunting and only do it when it needs to be done. As for the beast, the idea of it would have been discouraged, with all of the older kids saying that it doesn't exist. There would be no Jack-character saying that she'll kill the beast, which would be an argument completely averted.