12yr DD old quick temper

[omgwhatnext]

My beautiful caring thoughtful dd has turned into a quick tempered stroppy two headed demon who takes everything the wrong way, has zero tolerance for younger brother who just has to breath to have done something wrong.We used to hold conversations, now if she has something to contribute to a conversation she rolls her eyes and blows air down her nostrils even when grandparents are talking demonstrating her impatience and that clearly what she has to say is much more important that than the others, even if she has just finished talking. Help, how do i keep her on track?

I haven't a clue but my DD is 12 and we are really butting horns.
She is not naughty or rude its the rolling of eyes, the thinking she knows it all and the taking everything like its a dig at her.
She too has 2 youngers brothers..

I'm just putting it down to hormones but Its a nightmare!