I think all this is a plan of Maya
When Arjun told her hez leaving her in hosp.she planned all this
Vandana death is just a small part in this actual game
And for what revenge is maya gonna come back,when she herself knows that Arjun will come to kill her.when he will know that maya killed vandana.
So taking revange from arjun is not her plan
She wanted to kill vandana as she want to punish her
But her actual motive is to keep arjun with her
Which wasnt possible after babys death
So she planned all this she will kill vandana,make sure arjun will know she only killed her.will wait for him to attack her and stage her death.
Get him arrested for what just to make sure until shez back hez not getting hooked or married to sanjh.
Then bfr she comes will get him released by leaving some proofs
Then she will come with a new identity.
Then what he will be back of her to prove shez maya or to take revenge from her.
So in this way again she will make arjun back of her
I think this is her actual plan