This is a very strange case, as with LABs!
Deworming or Acidity might be an issue. You must be having an idea of what she likes the most. In such phase try out her favorite foods and something different from her regular diet. You may also try commercial dog foods like royal canin, Nutribix, etc. Give her small meals...that shall render her hungry soon again!! Be careful, not overfeeding her.
Do mention her age, diet and stool condition.
>> Visit a vet!!!