Hey guys, this is my prediction...
Shivam killed Vedika because she found out the truth that he was previously married and hid this fact from Niharika. Vedika decided to tell Niharika the truth after the party or maybe Shivam said he'd tell Niharika all the truth after the party and begged Vedika to keep quiet and once the party is over he'd himself tell Niharika that he was married. Vedika believed him and kept quiet, and during the party Shivam killed Vedika, just because he didnt want Niharika to find out he was married, because he was obsessed with Niharika and didn't want to lose her.
This is my prediction.
Lets see if this is the reason, because i don't see any other reason as to why Shivam would kill Vedika, plus Vedika is always the one who comes to know the truth about everyone first.
lol...Vedika the Great...
Yuvi😃