Short time voice loss could mean that she has an upper respiratory infection. Viral illnesses are also a possibility, particularly since she was boarded. If this is the case, your dog should recover with time. Keep an eye on the secretions from the nose or eyes. If they change color, the dog may need some antibiotics.
Long term voice loss could be a result of more serious factors and you should see the vet to rule out an obstruction, cancer, etc.
I am leaning toward the short term causes.
Let me know if you have more questions