my one year old cat is becoming more aggressive? PLEASE HELP!!!!!?

i brough a 2 month old kitten home exactly a week ago. about three days after, my older cat, Korra, seems to have gotten a lot more aggessive and she is generally a well behaved cat. she is now attacking other pets in my house and i dont know what to do. she hisses and scratchs at everyone and she pawed me in the face last night. that is something she has never done before. she also smells like she is sick. could that be part of the reason? i just want Korra to get along and i cant have her beating up my room mates dogs and have her kill my husbands ferrets. they all used to get along fine. i dont know what to do... PLEASE HELP!!!!