She did not react angrily to his allegations because in doing so she would only ruin any chances of putting her plan back on track. The old Madhu was hot headed and impulsive. The new one is cold and calculative. She had to maintain her cool while pleading with RK to not create a scene. When RK hit Sultan things were spiralling out of control and if Sultan had retaliated, things could have gotten worse. She then pleaded silently with Sultan to bear and grit his way through.
RK's temper had reached sky high by now and he unceremonious dragged her home to subject her to more humiliation. This is when Madhu's shrewd mind turned to the other suspect Dips, who was only too keen to fuel his doubts. Having already established that RK could not have called Sultan if he was to react so violently to his presence, she knew it could only be Dips. She very neatly turned the tables against her. Luckily for her Dips also did the honours of holding a mirror to RK about his own deeds. Now the guy is doubly guilty for having suspected her and would lie low for some time.
She saw her opportunity to give the slip when RK was taking the Sikki-Dips duo to task because she knew that the guy would dare not follow her immediately having made the blunder of doubting her integrity. Before his mind can awaken from the slumber it has been put into by his guilt trip, she had to go and make peace with Sultan. after all the guy had got hit and his parentage was questioned by RK and he was still clueless why he was subjected to this.