Purvi or Bulbul coming back with a new face using plastic surgery to violently attack and kill Abhi is ruled out. 😆 Firstly their enmity is more with Aliya than Abhi, and they are neither that evil / rich nor will they ever think to hurt their sister Pragya badly with such an horrible action.
Who can she be? An obsessed female fan stalker of Rockstar who couldn't get him or someone who has some old family feud to settle with Abhi's dead parents or a music career rival from Rockstar's early days unknown to the world or she may be linked to Nikhil / Dushyant or a relative of someone from Abhi's past who could have been wronged unintentionally by Abhi?
Now some one has to be wealthy enough to spend so much money to hire goons, a sharp shooter or a bomb attacker to kill a person that too bold enough to kill a celebrity.. and this ladies monologues indicate she has long suppressed vengeance directly against Abhi.
Based on Balaji's history, below is possible plot that was mostly used by Ekta's writers like Anil Nagpal in their old TV shows.
'Middle class soft spoken PA of a rich industrialist hero of Mumbai gets suddenly killed brutally one day and her brother from small town who is busy setting up an arranged match for his sister comes to know from forensic report and letter after his sisters death that she was used and duped by a rich guy and got pregnant before marriage. This middle class brother takes few years to build his own business umpire and comes back to Mumbai as new villain to revenge rich hero assuming him to be the guy who wronged his PA and responsible for her death. At the climax of the track original villain of the show i.e. hero's sister comes at nick of the time to save hero and clarifies that PA's rich boyfriend who duped her was another guy and her brother was innocent. She gets brownie points from hero and heroine due to this noble action'.. 😛