Short time voice loss could mean that she has an upper respiratory infection. Viral illnesses are also a possibility. If this is the case, your cat should recover with time. Keep an eye on the secretions from the nose or eyes. If they change color, the cat 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 because you are seeing coughing as well. If this continues, you will want to see your vet to get an exam and possibly antibiotics.
Let me know if you have more questions