Trust me, these foods ARE worth it and do make a huge difference.
A good food will improve the smell of the dog but, since the good foods are more nutrient-dense, the dog doesn't have to eat as much and hence poops less. It should also help improve her coat.
Be very careful with the blow dryer. ONLY use the cool setting and then on, 'low.' Dog skin is very sensitive to heat and same with the shampoos. You can get shampoos made for puppies at PetCo or PetSmart that have oatmeal in them and that's nice. I'd avoid the ones with perfumes in them. The smell can be overwhelming and if it's overwhelming to you, imagine what it's like for the dog!
Try to keep the water temperature at about 100F. That temp is very close to the usual body temperature of the dog and won't be as much of a shock. Puppies and small dogs can be very susceptible to drafts near the floor that we don't usually feel. Try to towel and blow dry as best you can and elevate her crate off the floor for 24 hours to make sure.
Make bath time fun! Get very excited and have a bag of small treats on hand and praise the dog for standing still in the bath. I highly suggest getting a hair strainer insert for the drain before you bathe. You'll find the hair strainers at the grocery store as well as a cooking thermometer to gauge the water temperature. At her age you can bathe her in the sink, but be prepared to have a lot of towels. You also want to get a rubber sink or bathtub mat. Many dogs feel very uncomfortable on the slippery surfaces of porcelain or stainless steel. The rubber mat gives them a grip and makes bathing less stressful. Don't go for the shampoo right away. Get the dog used to the water with lots of praise and a few treats for good behavior. Let her investigate the bathing area. Keep the entire affair upbeat and happy.
You'll want to brush her as well. Look on the shih-tzu websites for the grooming tools necessary to properly groom her. It helps to brush her before the bathing to remove loose hairs and to brush her afterwards during drying. There are doggy conditioners too and if your home has low humidity in winter then you may want to use one.
I assume you've had her to the vet already and the vet checker her anal sacs. If she smells more like rotten poo than dog, she may have blocked anal glands. Ask your vet about expressing the anal glands if that's the case. Sniff around her butt and see if there's a powerful stench and I mean STENCH, not just the usual anal odor. Some dogs have chronically blocked anal sacs which you can learn to empty. The blockage is usually caused by soft stools. Firm stools press against the sacs when she's pooping and cause them to release the fluid from the glands but if her poop has been soft for a while then there may not have been enough pressure against the glands and so they become blocked and inflamed.
