Is she being treated for GERD? If there is acid in her throat, she probably has GERD and the acid is coming up. This is serious, she should see an ENT. I had a hoarse voice, but my cause was thyroid cancer, my vocal chords were fine. If she does have GERD, is she sleeping elevated? This can keep the acid down, also she should not drink too much liquid at night, if she is breast feeding, I am sure her liquid intake is higher, but at night when she lays down, she should not drink anything. Sounds like the surgery is the one that prevents the acid from coming up, this surgery is important because there is a higher incidence of throat cancer in those who have acid reflux (GERD). I hope this helps.
What kind of med is she taking? Is it for thyroid condition?