Cat is being very aggressive and mean to other cat and she never was before?

i had this problem once its because you have a mother and daughter/son and mother is basically saying stand on your own two feet,try feeding them separately try giving them there own space to sleep and play and you might find in time it will stop what is happening.

I agree with bluemoo, it is probably just Mum saying time to stand one your own two feet. The only other thing to check for is that the mum cat isn't sick. Any cat that is sick or even just in a little pain will be very intolerant of another cat wanting to play. Just check her all over, check tahtnshenis eating and drinking normally. You also might need to make sure mum isn't in season. If all seems fine - just give them space and time. Make sure bothe have their own baskets or equivalent, feed them in separate bowls ( maybe even in separate room ) just so mum can have a bit of space.