What is the best shampoo and conditioner for my Shih Tzu if I want to keep her hair long and silky?

You might like this it's very good http://www.take1products.com All the best;^)
References :

I like Coat Handler products. You have to buy them through a groomers website or catalog. JB Pets, Cherrybrook, The Dog Outfitters are a few sites that will carry most or all of these products. A poodle breeder that I groomed for used a conditioner called Wu-Pi that was very good. My favorite brushes were Les Pooch-very expensive. For a Shih-Tzu I would use the small yellow brush. Also have a small fine pin brush and a greyhound comb. Best way to brush is lay the dog on its side, brush the hair backward then starting at the feet, brush a little down at a time-like a part to the skin..then work your way up the leg (this is called line brushing). Once you brush the whole dog like this then do the same by combing.
References :
Breeder, Groomer, Handler, Boarding Kennel owner

Check with a good groomer. I have 3 long haired shih tzus and their hair is beautiful. They go to the groomer ever 2 weeks. I leave the shampoo up to her. She used to show dogs herself at Westminster and grooms a lot of long haired dogs. I applaud you for putting in the effort to keep your dogs hair long. Shih tzus are absoultely beautiful when they have long hair.
References :