2yo DD is so aggressive!

[CDMforever]

I have 2 DS age 4 and 13 and 1 DD aged 2. Obviously the eldest is rarely involved but when the two LOs are together all hell tends to break loose and its 99% down to DD starting a fight - pulling hair or sratching her brother's face mainly.
Her speech isn't as forthcoming as her brother's was at her age and I know she can get frustrated but this doesn't seem to be the thing that prompts the horrible behaviour.
Equally worrying is that when she does hit or scratch etc she doesn't respond to any reprimanding. We've tried putting her in the "naughty cot", shouting,making a huge fuss of her injured brother but nothing seems to change her behaviour.
Is this just terrible 2's behaviour and I've been incredibly lucky with my boys?
Her character is very strong. She never backs down and jumps into everything metaphorically and literally!

Anybody out there????????

Hi
I just registered today for help and your post is exactly what I was going to write myself!!

We have a little boy of 2 year 4 months and daughter of 6. Charlie's constantly terrorising his older sister.
She cant play in her room or play with toys or even watch the TV.
After a couple of minutes together he will start scratching,hair pulling and the occasional bite.

He's really demanding on us and at times we struggle a little. Any ideas would be welcome?
As you said before about the 'Naughty Cot'
somebody else has told us to do that.
May give it a try.

Hi dano, spoke to my childminder today who said "Ignore bad behaviour, reward good behaviour". Will give it a whirl!