It is possible some of this could be staining caused by moisture. Does she drool a lot?
I have a dog that is nearly twelve with health problems that make him drink often. Lack of teeth cause his tongue to hang out and so his mouth, chin, chest and paws, where he rests his head on them, are frequently wet and become stained pinky brown.
Try keeping those areas dry and carefully rub a little talc powder into the stained areas.
Cavaliers......Faith, The Ginger Tank and Woody.
Japanese Chins.... Dandy, Benny, Bridgette and Hana.
Remembered with love......... Tommy Tuppence and Fonzi