Ask a Dog Vet and Get Answers to Your Dog Health Questions
It sounds as if your dog's fur is becoming stained by her saliva. This is very common in white dogs and is purely cosmetic. There are some products that are marketed as being able to reduce tear staining but nothing is approved for this and there are no clinical studies to support their use. Some are safe, but others may be harmful if used incorrectly. The best recommendation I can make is to keep her fur clean by using a gentle eye flush to clean the corners of her eyes daily and trimming her beard. You can use Bausch and Lomb contact lens solution (Renu) to clean her eyes. If you want to try something you can give her with her food, some people have reported success using a product called "Angel Eyes" or a probiotic supplement called Proviable. These are fairly safe and available over the counter.
If she has excessive tearing, you can speak to your vet about an eye exam to look for causes of irritation the cause excessive tear production such as eyelashes that are growing into the eye.