My guess is that the producers wanted B to take Sonja under her wing for a storyline. "Can the most brusque, straightforward person on earth get through to someone who's arguably diagnosable as delusional?" And that B was ok to try bc she genuinely likes Sonja and remembered from years ago how sweet Sonja was. Bc otherwise, it's pretty bizarre that someone as narcissistic as B would try to help ANYONE. Usually, B makes it all about herself 100% of the time.
I think as a rule RH would be much more interesting if B was allowed to talk about anyone or anything besides herself. I'm so tired of hearing her talk about herself, her daughter, her divorce, her past or her brand. But I think she's generally clever, insightful and interesting when talking about ANYTHING else lol