White cats with blue eyes have a higher-than-average tendency to be deaf, but that doesn't mean it only happens to blue-eyed kitties. It's something in the genetics. Have you done any testing, like snapping your fingers when she cannot see, and seeing if she reacts? Might be something to have the vet check next time you are in. Even if she's completely deaf, doesn't mean she cannot live a great life, but I wouldn't ever let her out unsupervised or off-leash - the world is an even more hazardous place when you cannot hear danger coming!

Kittens are funny, I have heard of others who "sing to their supper" as well!