I'd say she could be bluffing, except she does almost draw on him

I'm pretty sure she's lying because by that point in time, she knows by then to not mess with 'fixed points', so between the S5 finale, and 'Time of Angels' and 'Flesh and Stone'- she can't let out anything that she does already know them, and how she knows them- because there's already a 'set point' in time for that.