i feel after divorce if ashok has married her then she wouldnt have bothered raman more.
after raman tauting her that now she is nameless(i.e no surname) etc she became soo insecure.ashok laid condition tht shld get ruhi custody for marriage.in the process of custody raman taunted her badly.she is nt able to accept that the person who loved her madly once is taunting,insulting her and comparing with ishita.
before this taunting only ashok want to revenge raman but due to tauntings shagun herself want to revenge raman.so now she is completely concentrating on revenging raman.
so everything started with ashok