"Is that so?"

She doesn't have to feign surprise- and a good thing, considering her acting skills. But 'between you and me' likely meant 'between everyone listening' as well, so she isn't willing to be too enthusiastic just yet. If it were 'play nice and it will work out' she may just have to storm out of the room before she was forced to throw the desk on top of the other woman. Still....

"I am listening."