Translation:How is your grandmother?
In Japan it is impolite to address someone as you. So you will rarely hear anyone saying "anata" or its variants while talking to them.
They are usually addressed in 3rd person. And as Julian Beasley said, it is a very well accepted way of asking one's grandmother, or any old lady, " how are you?" Or "Are you fine?"
That's a more literal translation, but in English we almost never ask, "Are you well?". Instead, we ask, "How are you?"