Aggression with our Rescue Dog

Question
Hi Robin.  We adopted a 3 year old Boxer/Vizsla from the shelter 6 weeks ago.  We chose her because we have an almost 2 year old son and she was suggested as a "great, easy going family dog".  She was awesome with him our son, and other kids, the very start.  The first few dogs we had her around she was fine with, but after a few days, she tried to play with a cocker spaniel who didn't want to play and she's been dog aggressive since.  
If we walk past a fenced dog, she jerks on the leash, jumps at the fence, barks and it takes all I've got to redirect her.  If a dog walks past our house, she scratches at the window and barks like crazy.  Occasionally, she acts the same way with a person--she fixates on getting to them.  It's not a certain type of person or situation (though I've only seen this out on walks), so there's really no way to redirect her before we scare the bejezzas out of them.  I don't think she's out to bite, but I'm not willing to see what her real motivation is.
I've been working with her every day walking with treats and positive reinforcement.  I just got a gentle leader and have used it once.  Some days it seems like things are getting better, some days it seems like it hasn't changed a bit.  
(One other thing that seems like it's connected is that she'll come up to the door to come in and when I open it and call her in, she turns away.  I have to leave it open and let her come in on her own.  On the other hand, she sits and stays like no dog I've ever known.)
I'm starting to question if I'm doing everything wrong, if things can change, and, ultimately, if we can trust her with our son.  Last night, she ran into him full blast.  I think she was playing, but she's played "chase" with him many times before and has always been careful NOT to plow into him.  This time, she purposefully knocked him down.
We can't afford the $600 for an animal behaviorists.  I've pulled some info off of the Internet and have tried some ideas from books, but I just don't have time to search through and implement everything.  I can't bear the thought of taking her back to the pound, but I also hate worrying about what's going to happen next.  I don't want the neighbors to be scared of her and the mom in me says we can't have a dog that doesn't listen around our son.  
Please help!  We've never had a mean dog and we obviously don't know how to deal with her correctly.  We love her and don't want to give up on her if there's a chance we can get things right.  Any advice would be appreciated.
Thanks!
Ashley


Answer
This is going to take time, I'm going to warn you right upfront. I am not 100% sure this is aggression, but it definitely seems like dominance confusion.

First, carefully practice the tips you find here: http://www.thegooddogjournal.com/2009/02/whos-boss-establishing-pack-leadership....
Teach them to your whole family and make it a habit for everyone.

First, you need to obedience train your dog. Make sure that she will sit and down on the first command and knows how to walk nicely on the leash and automatically sits when you stop walking. She should also be able to sit in a stay for a full five minutes. It takes me five weeks to teach my clients' dogs these things. I only see them once a week and my clients practice every day.

In the meantime, before the full foundation is in place, take your dog for daily (preferably twice) walks around places where you know there are dogs and people, but take care to be on the other side of the street or far enough away that you can continue to walk and do. Just walk. Ignore the dogs' nonsense and continue forward like nothing is going on. If another person or dog is approaching on the sidewalk, cross the street.

With that firm foundation, you can begin desensitizing your dog to the presence of others. Have some helpful neighbor with a dog approach in neutral territory. Your dog should be in a sit and stay. As your neighbor approaches slowly keep an eye on your dog for signs that she is becoming agitated. Just as she become agitated, have your neighbor stop and put her dog in a sit stay. Have your dog sit, down and stay for a few seconds, give her a treat and then have your neighbor walk away, circle around and approach again from a different angle following the same method previously described. Repeat 10-15 times a day, having your neighbor get a little closer on say the 10th repetition each day. To be clear, don't start out closer than last time but get a little closer halfway through and start there next time. If it every becomes too much, have the neighbor back up just a little.

For your people issues, you will need another volunteer. Have the person approach slowly, looking up at the sky, hands in pockets. The minute the dog gets hyper, the person should stop. When the dog is calm, the person should proceed forward. Continue until the person is just beyond the reach of the leash and the dog is calm. Then the person should throw a handful of treats on the ground where the dog can reach. Repeat three or four times or until the person can walk right up to the dog without her getting crazy. Then she can try petting. Have the person reach underhand to pet the dog's shoulder, not overhand to pet the head.

Your son should be very firm about when he will play with the dog. If the dog is hyper or crazy, your son should refuse to play with him or even look at him. He can get up on the couch and pull his arms and legs out of reach (the dog should not be allowed on the couch). Your son should also practice giving the dog commands and rewarding the dog for obeying. These should be supervised interactions. If the dog doesn't obey, you should enforce the command.

This is your plan. A reasonable timeline is about three months. Ask yourself if you can make this commitment?