I have different point of view... She is real culprit for hiding truth from Yug when they become friends... But there circumstances to be blamed.. she knew that Yug is searching for girl having that voice.. but same time she knew that he knows her name Gauri Jha.. in such case what she should have revealed?? That she was actual singer of song and price was taken by Gauri?? And why someone reveal so much personal matters to Person whom you met few times.. To take credit of ur voice which she never done before...
Now coming to telling truth to Yug before engagement.. she was one who everyone would have blamed.. For telling truth to Yug.. even right now she hasnt revealed it herself.. Gauri is blaming her.. thats why she asked Gauri to say it before its getting to late for marriage. This truth should have been told by Gauri as she is one who is getting married to Yug. some other person giving information about ur partner is obviously not correct way...
From Yug perspective she is one who hide truth.. but considering current situation that she is kaala teeka of Gauri she knew that there is no future for her and Yug.. when people know their family wont support love with someone people dont confront it... Right now she is in bad situation as her family has selected Yug for Gauri..