Loredana, perhaps she's acting this way with you because she trusts you. I know that my puppy was also biting me the most at 3 months, because I was the person feeding her and doing everything around her. So if she wanted something she would show me by biting, so perhaps you also need to teach her other ways to show you what she wants, e.g. by sitting by the door when she wants to go out etc..
As a rule dogs become possessive when you take things away from them. So never never never never take things away from dogs, that way they never learn to be possessive. Instead of taking away things, either reward with food or treats for giving the toys to you, or just give them more things.
So when you want to take away a toy, show her some food/treats and see if she drops the toys/things, only then take it away, and reward with more food. Even your dog chews on your shoes, ask her to "leave" first and then reward her for "leaving".
I highly recommend doggie zen for teaching dogs how to leave things. Once they know the word when you teach them with pieces of dry food (perhaps it's better to teach before dinner when they get a little hungry, and also don't worry about doing all steps at once, start with 2-3, repeat 2-3 the next day and add another 2-3, and so on) , the knowledge should easily transfer to other situations: http://www.dogforums.com/dog-training-f ... y-zen.html