Hi DorothyL, I am in the exact same situation - we have three children 2 boys and the middle DD aged 11 nearly 12. She started her periods 3 months ago and is as you describe with your daughter.
Sometimes can be lovely, very caring, but most of the time, just nasty and rude. So much sarcasm and attitude and I am astounded in the way she speaks to me sometimes (and my husband, her brothers - its not just me!).
When I ask her why she is being so rude she doesnt seem to have an answer and will just walk off / cover her ears / do her own thing.
She is in year 7 at school and very easily distracted in class which is causing problems. Regular warnings in class from the teachers for not concentrating and when I talk to her about this, she doesnt seem to realise the longer term implications.
I find her so horrible at time, it really upsets me that my lovely daughter would behave in such a way.
I've also heard it may pass... but if we have to wait 2/3 years I worry by then things will have really escalated by then and would love to know how to nip it in the bud now so we can all enjoy eachothers company and not be arguing all the time.
Even yesterday when I was talking to her about her behaviour, she replied 'yes Miss' .. with such sarcasm. When I picked her up on this, she seems to be oblivious to how rude she sounds.
Its awful ... would love some tips of how to get through this if anyone can share some!