A little bit of pondering will make this crystal clear. Tappu Baba, like all of us in this forum clearly know that Veer was carrying her like a burden even if he never thought her his wife only because of Vansh. And now when Vansh is no more there is no way or any reason to carry this burden. So running out of options, with the evil/devil mind that she has, Tappu baba did not hesitate to compromise with her dignity and self-respect (unfortunately this well thought out disgusting act is celebrated as love and consummation). This is further strengthened when she decided to start plotting to create more mis-understanding between so that she will do more such thing in future......is it Love??? Our forum members are wise enough to differentiate between love and plot.
Yes, the bottom line is Tappu did it not out of her love, but simply she had no option but to play another dirty game to capture Veer by hook or crook or fraud, or deceit or criminal act because the very reason for which Veer was forced to be with her i.e. Vansh is gone.