First and foremost, you are spoiling her. You need to take control. The reason she begs for food, is that you give her food. No one should have to lock the dog up to eat.
You need to establish that you are in charge, by not allowing the behavior.
No getting on the couch. No jumping up on you. Don't yell and fuss at her when she jumps up, simply push her away, and ignore her. When you want to snuggle your son, do so,a nd ignore her, if she is pushing in, push her away, tell her no. A sharp hist! will work better than out-shouting her, as shouting is just going to make it a game.
When she is acting calm, you can give her attention. No treats to make her behave, she has trained YOU to give her treats. Consistancy is the absolute key. Both you and your husband have to agree. When you come home, do you make a huge fuss? You are teaching her to act wild to get attention. Be calma nd pretty much ignore her until she calms, then pat her and swcratch her. Make her sit to get attention, and work on one or two things at a time. How does she get exercise? She NEEDS loads of exercise. A walk, won't do it for a atlethic breed like a boxer(or in this case a boxer mix). Get her to jog beside a bike. Teach her to walk on a leash properly too. Leash training is simple.
One chain coller, one 6 foot leash. Attach properly to dog. Go outside. Start walking and when the dog passes your leg, turn around. The dog will hit the end of the leash, come up short, whirl around and head the new direction. Again, when he passes your leg, turn around. What you are teaching is that you are unpredictable, and that the dog needs to pay attention to YOU. Once you can walk with her beside you, you can refine that to heeling, NEVER NEVER hold the dog nearby you! That ends up being nothing more than a tug-of-war. You let the dog go,a nd tug them back into position, then give them slack. If they move out, a tug back then slack. You MUST give them the opportunity to make the mistake, so you can correct it. Note that I do NOT say SNATCH them back, only tug them back to position. The slip chain collar is to prevent them from backing out of it, and it give enough of a tug consistantly.
Start with that, I've retrained tons of dogs. Be in control, and they will behave.
Wolfy