The Goq; She is not conversing with Hashem. My husband tells me her husband who is 13 years older then her, and one of their sons who is divorced does the same thing. The divorced son starts talking to himself when something in shul annoys him. For example, if the Ba’al Tefilla is taking a little to long, etc.
Psychology 101: If you are talking to someone and during that time he/she is mouthing something, it is a supposed response to what you are saying without listing to what you are really saying.