How To Stop A Nightmare Kitten?

katie, i have a kitten that is pure nightmare. she has been in the same house for about 5 months and all of a sudden 2 weeks ago she started to get meaner and more aggressive….i think it was because my boyfriend got rid of another cat from our house…the other cat had kittens this winter so we took care of them until they were old enough to leave..when he got rid of her though, my nightmare began…this little girl did not like us at all! any time we tried to pet her she would hiss or scratch us which hurt quite badly! but lately it seems as if she gets worse every day. today when i was talking with her it seemed as if i didn’t even exist to her ….she just stared back into space …i couldn’t see what made me different than everyone else!!!! now ive noticed that sometimes when im sitting down on the couch or something, she will start attacking me through the arm rest (which is solid wood) ..its very frustrating!! please help!!!