Presumably, soon after the events of the "The Doctor's Wife," the TARDIS gained a holographic interface. We've seen ("Let's Kill Hitler") that it can change its appearance.
Why does the TARDIS choose to mirror Clara when it speaks to her in "Hide"?
The visual interface states "I am programmed to select the image of a person you esteem". Clara has also stated that she feels that the TARDIS doesn't like her. It might be that the TARDIS wants to annoy her by saying that, of all people in the world, Clara only holds herself in high esteem.