For the sizes they are offering on ebay, those are not good prices.

I go between Petco, Petsmart, and http://Chewy.com. Whichever one has it the cheapest is where I buy. I have 3 large dogs and a frugal husband, so getting a good price is essential. Chewy and Petco both offer repeat delivery options which will offer an additional discount. Also, if you shop at Petco and you are a Pals Rewards member, you will earn $5 rewards for every $100 spent. Two bags of dog food and you're there! You can then turn around and use the rewards on your future purchases lowering the price even more.

I found several recipes on Pinterest. I substitute tapioca flour for regular flour (it's gluten free). You just have to use a little more than the recipe calls for.

Nylabone has some tough toys that have stood up to my Boxer/Lab. He is an intense chewer! We also have the black Kong and he has yet to destroy that. We give that to him with frozen peanut butter.

I would recommend agility, or puzzle games. Agility is great for a really active dog, as it gives them some kind of job to do. Puzzles games are great because they stimulate the mind while the dog works for the treats. Unfortunately neither of these is something your dog can do without your assistance, or supervision, but they will help to wear her out so she will be less stimulated when you're not with her.

You can make frozen treats out of plain yogurt and pumpkin, or peanut butter. Fruits and veggies are good, as long as they are dog safe. I also give my dogs Whimzees as a special treat when they will be alone for a few hours. They are vegetable treats you can get at pet stores. They come in cute shapes like toothbrushes, hedgehogs, and alligators.

Have you tried agility? There are some reasonably priced, small agility kits out there (tunnel, hurdle, weave poles, etc). I got one from http://Petco.com a while back. My dogs love it!

You can add coconut oil to her food. Start with a teaspoon for about a week, then slowly increase to one teaspoon per 10 pounds of dog. It won't completely stop the shedding, but it will help. You will also see her coat get softer and shinier in a couple of weeks. You will still have to brush her, but you will find the brushing will be less often.
One important tip: use only cold pressed, unrefined, organic coconut oil. It comes in a solid or pasty form (kind of looks like lard in a jar). Just heat it in the microwave for about 20-30 seconds and it will become liquid and make it easier to mix with her food.

You can add coconut oil to her food. Start with a teaspoon for about a week, then slowly increase to one teaspoon per 10 pounds of dog. It won't completely stop the shedding, but it will help. You will also see her coat get softer and shinier in a couple of weeks. You will still have to brush her, but you will find the brushing will be less often.
One important tip: use only cold pressed, unrefined, organic coconut oil. It comes in a solid or pasty form. Just heat it in the microwave for about 20-30 seconds and it will become liquid and make it easier to mix with her food.

My Shepherd did this when he was a puppy. We put the water bowl up off the floor (where he could still reach it to drink) and that solved the problem.

If your Shitzu is the only dog she is used to being around, it may be a socialization issue. As Lindsey said, dog parks can be very overwhelming. I would try socializing her with friends, or family members dogs and see how she acts. Do this on neutral territory at first, to ensure there aren't any territorial issues.