Dog Health Questions: Difficulties with dog training?

I've been having issues with my puppy and reigning her in. She is a 6 month old boxer/german shepherd mix. We've taught her sit and lay down. But whenever she does it she runs around and does it halfway. We only treat her when she does it right, but she still won't stop. She also basically uses our kitten as a chew toy, sitting on her and mouthing her. I feel like she might be hurting my kitten because of the vast size difference. And one last problem is that she chews on everything in the house from walls, to her bowls, to my table and chairs. she always has several toys around but she goes for the things I don't want her chewing on. I've sprayed things with bitter apple spray and I praise her when she uses her toys.
Any suggestions on these things?

So You Want a Guard Dog, Eh? (Basic Dog Training)

Recommended Answer:
Crate her when you can't supervise. When you can supervise, keep her on leash and attach it to you. She can't run around when you command her to do something if she is attached to you.

Advanced Dog Training Goals - It Pays to Think and Plan Ahead

• Like many undesirable canine behaviors, destructive habits usually develop because a dog is bored, lonely, or both.
  
  Try to link to get more tips on how togo about it:
  http://dogtime.com/chewing-digging-behav…
  
  As for the trainining, I think it's a good start if you start with crate. Be upbeat about putting your dog in his crate, and when you return to let him out, be matter-of-fact about it. If you act like it's no big deal to be in the crate, your dog is more likely to act that way, too. It's also a good idea to put him in the crate for brief periods even when you're home--that way he won't link being alone with being in the crate.
  
  Read more abt this: http://dogtime.com/housetraining-crate-t…
  
  goodluck!


• Ok Below are somethings you can do:
  
  1. Say you are going on a trip or to work then you crate her in bar crate which you could get a any local pet stores or even online.
  
  2. You could take her to classes to train her, they might cost money but it is worth having a good dog.
  
  And below there is a website asked by another person who had the same promble:


• It sounds like your dog has some basic obedience problems.
  
  I don't know if you're familiar with the concept of "being the pack leader" when you get a dog, but it sounds like your dog thinks it is a high-ranking member of your family. It would make sense for the dog to think it is ranked higher than a tiny little cat.
  
  Next time the dog starts playing too rough with the cat, make a loud "No" and pick the cat up and start giving it praise/attention/food.
  
  Also, make sure your praise is handed out with precise timing so the dog isn't confused as to what it is being praised for. You may also want to consider a complete dog training guide to cover obedience/aggression/chew training. A good guide will open your mind to things that may be the cause of these problems. Seperation anxiety maybe? I've linked to a site with a few articles and guides in the resource box. I hope they help.