IMHO
You talked to your daughter, explained what is expected of her and what she should and should not expect from friends...to me, thats the end of it. You did right.....
as far as the others....
getting a school principal involved, and adults all gabbing about it, is wrong.
The school had no business knowing this information..it did not happen there.
By NOTIFYING the school, "talking" about it amongst the parents...(lest I say gossiping) is wrong on more than one level....
To talk about things that allegedly happened, can lead to a very slippery slope (have an umbrella policy to cover possible
slander 
for instance....)
why make this childs life any more difficult than it already is...she apparently has some anger/control issues and lets hope she gets/getting Help....
Id say remove yourself from the situation and move forward away from it....