why is my dog aggressive to people and dogs?

[Black C]

i have a four to five month old pup who i have taken to puppy school and has been well socialized with dogs and people but she has become very aggressive towards dogs, people and cats including myself and my family she has gone for peoples faces including a young girl as she can jump quite well can anyone tell me how i can fix this as i have young family members coming for x mas i don't want to put her to sleep only as a last resort