Kat practices Domination as a lifestyle, but to do it effectively, she needs to know the psychology of her subject(s) in order to develop a proper training plan, else she's liable to use the carrot/stick at the wrong time or wrong severity. Whether we humans like it or not, our background dictates much about our personality and character, either in agreement or rejection of our original values, so naturally she checks MC's upbringing, and finds a hostile and protective response from her subject regarding his mother. Here she kills two birds by 1) gaining valuable background information, 2) discovering a soft spot or "pressure point" in the MC. Another critical part of her discovery/training regimen is to isolate the border between a subject's compliance and resistance, thus she has to deftly press on the subject's limits just until she finds the point where they finally snap back. Her goading of Rose to the point that Rose slaps her is a perfect example. For MC, she discovered the pressure point in the limo, and then pressed his limit before the studio shoot. I suspect she's satisfied, at least regarding MC's position on Victoria, so she won't press the issue again, unless it's related to his sadistic limit (like the conversation following Week 2's Exhibition).
