Let's say that sheetal isnt in league with Mishty which is what most of us are assuming. lets pretend what we see is true- no behind the scenes stuff.
sheetal is telling kripa exactly what she sees. She is not making anything up and from the way Angad and Mishty are together- the way mishty wants him constantly, it does seem like he is giving his "mardangi" for money.
secondly, as a friend sheetal should tell kripa what is going on BUT kripa should not just blindly assume the worst from sheetal's info. she should trust in angad and find out the truth- after all she knows enough about misunderstandings to see that sheetal might be mistaken.
lastly, angad should stick around mishty considering their past. and he knows kripa doesnt like it so he should repect kripa by keeping away from mishty. its not like he can only work with her. and if prithvi woke up and pretended to be good and kripa became friends with him- wouldnt angad not like it and assume that something might be going on if shabir were to say that he saw kripa and prithvi hugging?
so sheetal is not at fault as far as we know.