Try a different shampoo, I use "Dirty Beastie" by Wahl (professional) for my son's Yorkie, he smells awful - it starts with his feet! I have to bath him much more than my Pomeranians as he makes them all smell, seems that Yorkies are smellier than some other breeds. Also, use conditioner, lots of it, to keep the coat sleek

Try Brewers Yeast tablets to help thicken her hair,you can get them at health food shops.

I have four Yorkshire Terriers they don't smell at all and they have thin and silky hair. If the hair turns coarse it could be the dog is missing some grease in its diet. It could also be that you are feeding it with stuff that has too much flour in it like bread, rice, pasta, biscuits or perhaps potatoes. I would suggest you feed it with natural food four times a week and dry food for the rest of the week and switch the meals day in and day out. Be careful with the dry food use lamb products others make their hair real greasy. Check the label if too greasy don't use it. Yorkies have liver problems, if you feed them with greasy food they will get sick. They need a bath each 20 days, a good shampoo and conditioner, be sure to use non greasy products. After the bath and before blow drying it, be sure to clean the inside of its ears, ask your vet for anti ear mite product and an anti flee product that you rub on the back of its neck once dry. Never leave it wet after the bath as they are usually cold and thus try to put their temp up by heating themselves and that could make them smell. Brush its hair if possible daily, be sure the brush is washed clean. Every end of the month it needs to have a nail cut, be careful it is easy to hurt them if you don't know how to use the pincers. Don't let them grow too much or the cuticle under the nails will also grow and then it is very difficult to keep their nails short. It would be better if the vet does it and also gives it a monthly dental cleaning, they suffer from tooth decay. Don´t forget to change its bedding day in and day out, no need to wash them put them somewhere out in the air or sun. When you give it a bath change the bedding for clean ones. I do this myself, when I have sent them to a grooming center they usually use a lot of perfume to cover up that they have not given it a good bath. I also take them to the vet once a month. Sorry I know it is a lot of work, but that is the price to pay in order to have nice and none smelly dogs. Regards.

obviously, a vet checkup would be advised .. it could be cancer etc if these other answers dont help..seek professional advice

You may also want to use baby wipes and just wipe her down. Change her diet that's probably what is affecting her coat. I would say buy science diet and buy some chicken breast. Boil the chicken yourself and mix it with the science diet dry food or even just give her chicken and chicken broth. This will help her coat and the smelling should go down. Also buy non allergenic shampoo at pets mart. This doesn't have any scent, you don't want to throw perfume into the mix, then it will make the smell worse.