When one is asked with a sound question, or hit with a cold hard fact, when blinded by anger, those kind of people tend to lash out, as it's the only way, they know how to act, but Beatrice had lived for far too long to be that unwise.
So when Lily asked her a sound question, she paused, backtracked and thought things through clearly. First she looked back to the kind of person Lily was from the moment she met her. To her she saw Lily, as cold, calculating, unfiltered, but also has some hint of kindness in her.
The kindness she saw whenever Lily looked towards her friends, as each time her gaze becomes genuine, but since she's calculative, Beatrice doesn't know how much she can put her trust in that gaze.
She started recalling to when Lily's face cringed when she saw the bottles of wine, and her gaze glistened with disapproval for a moment.