Why is my female budgie attacking the other budgies?

Hi I breed budgies in an aviary in Australia and I have currently 4 adult budgies (2 female and 2 male) and 5 baby budgies (3 baby's have fledged) but recently 1 of the female budgies is attacking the others in my outdoor aviary. I don't understand this behaviour but I guess a have alot to learn, but I also have another female with still 2 chicks to still raise in the nestbox. I have 2 nestboxes On the same height level. But the female that's attacking all the others mainly attacks when another bird goes near the mother budgies nestbox like she is guarding the chicks even tho ther not hers. Does anybody understand my female budgies behaviour, if do please help me out