You have to be very gentle with your furkid due to the age, when a bit older you can use whitening products but not really right now. With our dalmation I have used a 1/2 cup of regular bleach in the FULL tub of bath water, she was always brilliantly white. With my Papillion I used beauty products called Bluing it is for older White Haired women and men, you can go to any beauty supply place and ask the ladies there for the most GENTLE available and instructions, but again wait a bit before you use it on the little girl. It is a shampoo and you leave it in the hair NOT on the skin. Lucky the paps have such long feathers on their legs it is not that hard to do....
One last suggestion, with long haired pups the desire to wash them frequently is there but not a good idea. You can develope an allergy or contact dermatitis if you strip all natural oils from the skin and hair. Many of the Handlers we know showing a white coated breed use talc to both whiten and fluff . With puppies it is all things in moderation...
Any pictures of her?? How about her name, come on share 
Bonita of Bwana