True Madhu doesn't know the complete picture because neither Radha nor RK has disclosed what makes them be like that . Both has shared a part of their story with her not the complete picture. In a way both are still avoiding the real problem in their lives and that is Kuku Bhatia and his family. Radha thinks she has a happy family where only RK is not happy. She doesn't want to admit why RK is not happy neither she wants to face the truth.
Well after watching the episode it made me think why Madhu brought his mother in this. I think she kind of wants to justify herself RK's test on her, making her heart believe it is because of his past his insecurities that made him do that. But as soon as she talked about his past, she again remembered her test and the doubts started in her mind whether RK really love her or is this part of the revenge. So the way they have brought this Radha angle into this MU was I would say not that bad, though I would have preferred it was never brought up.
I don't think at this stage Kuku Bhatia will come in to picture. Maybe for now RK's past is wrapped and is closed, though they have given an incomplete closure to it, maybe for now this is about RK's past.
Even I wish this MU will at least put an end to RK of letting go of his past with Dipali.
Till now, it was RK who was twirled in his insecurities but now Madhu is too pulled inside.
Maybe RK has come out of his insecurities completely. But as you said Madhu is pulled into insecurity of her own by this test. And it would be really hard for her to come out of it. And I don't believe she can come out of it soon.