Dogs don't feel jealousy like humans do. From what you describe, your dog believes she is the pack leader and is merely behaving like a normal dog - who happens to be the pack leader. She sees you and beneath her in the pack order, so in her mind she's "protecting" you from your son.
The idea behind "showing her who's boss" is where you need professional help. The word "discipline" has unfortunate negative connotations. Many people assume it means physical retaliation for breaking household rules, and that's a gross misinterpretation. All you need are some basic communication skills with your dog in order to establish that she's on the bottom rung.
This can end up being a serious problem if you don't address it properly, and soon. Growling at your son is only a symptom of something that can soon become dangerous. Any dog, no matter how small, can inflict damage on a person. The more your dog feels established as The Boss, the more likely it will be that she bites you, your child, or another person out of a need to defend her territory or pack. I am deadly serious when I advise you to obtain professional help from a behaviorist. You can't wait until your son is older; you have to address the problem now.
thanks for your comment. she gets lots of love and affection but i think she is jealous of my kids more so of the younger lad. b4 i had my youngest son she had all my time and attention then when i had my little boy all that changed. for the first 2 years of her life she was spoiled she is a lovely dog but you are right i need to show her who's boss! but i think when my little boy gets older she won't be as bad, she often growls when he goes by her, i think sometimes that she thinks shes human and likes her own space, like the rest of us!
Well I had the same problem with my male jack russell also same age as your dog, I found that he was becoming very dominant, be sure to get him checked out for behaviour problems, you have to let her no who is boss, start with more exercise and play time then go from there if you find she is getting worse get a behaviourist specialist good luck .
Both the title of your post and your final sentence tell me everything I need to know. There are no "bad dogs"; but there are dogs who don't understand house rules. It's up to the owner to both learn how to "speak dog language" and communicate those rules.
You are correct that your dog is ruling your roost. When there is no reliable leadership in the home, any dog no matter how large or small, will step in and fill that leadership vacuum. That means that you and your dog must go back to basics and learn what should have been taught in puppy school. Your children must also be involved in this process if it's to be successful.
It's not true that an old dog can't learn new tricks. Sure, it may take them a tiny bit longer to figure out what you want them to do, but not much. While you can accomplish a great deal toward taking back control of your home through reading books and watching videos, professional help is really what you need now. Basic obedience training alone won't accomplish what you need, so seriously look into a veterinary behaviorist. That's the person who will teach your entire family to be pack leaders who will take back the leadership role in the home.
Dogs need structured exercise just like small children do. If she's not getting walked regularly and properly, she's going to be a very frustrated dog, and frustrated dogs can be destructive dogs. A dog who is walked on a 25 foot flex leash and allowed to do whatever she wants will not get the mental exercise needed to drain energy and establish your own leadership.
Can you explain how you handle some of the situations you have described? When she growls at the kids, what sets her off and what do you all do to either prevent it or stop it? Is there any discipline in her life at all, and what kind? (Discipline doesn't mean hitting or slapping.) The more detailed information you provide, the more we can help, but you still need a pro to see exactly what is happening to achieve the best outcome.