Dog Health Questions: Dog training/gaining back leadership Help?

Hello i am a proud owner of a female toy chihuahua who has a bit of a problem and has no knowledge of how to change it. My chihuahua is about 9 years old and i believe it is the ways she was trained and not trained. Before i start id like to say she is not a bad terrible dog, she is very attentive and listens and is house broken and knows tricks, but she has some anger issues and will sometimes rebel commands to i or some other of my family members Except my dad and mom.
Her are the things id like to learn how to control and gain the superiority back:
1) when going near her bed or food or near her while shes laying with my mom shell growl and glare her teeth and sometimes snap bite, i say no but she doesn't listen,its agreesion issues.
2)Shell bark at every new person to her that steps into the house or when the door knocks, im taking it she doesn't have any socializing experience with humans or dogs, our fault...

Is there still hope at her age to teach her how to be obedient and not aggressive? can we train her to stop barking and growling at every person who comes into our home?
or is all of it to late to even attempt train her? please help? any methods or advice, i would appreciate it thank you.

Get a Well Trained Dog With Dog Training Guides

Recommended Answer:
On the contrary, every dog can be trained no matter what age. I seriously suggest finding the show It's Me or the Dog. Victoria Stilwell is the host and she's very smart and good with trouble dogs. A lot of the dogs bark at the door and she has a great method for training. :)

6 Dog Training Tips For a Well Trained, Well Behaved Pet

• Obedience training is the foundation for establishing a better relationship between you and your dog. Obedience training helps establish the owner in the role of "pack leader". Obedience will lay down clear behavior guidelines that your dog can follow. A well-behaved, obedient dog is more than just a pet of pride. The difference lies largely in the training, and good training can save a dog's life.
  
  These articles will give you tips about how to best train your dog.
  
  Dog Training - http://www.dog-pound.net/dog-training.ht…
  
  Dog Obedience - http://www.dog-pound.net/dog-obedience.h…
  
  Repetition, consistency, practice and correction are what it takes to train a dog to be happy and responsive. If you follow these simple steps you will find that your puppy can grow into an obedient well-adjusted dog.
  
  Repitition and Consistency in Dog Training - http://www.dog-pound.net/repetition-cons…