If we think about it, it wasn't the bad omen thing that made her fake her death and stay away from everyone she loved. Vidyut had evidence that prakash murdered neela, and even though vidyut told her he was drugged and forced to kill neela, he had even explained to her she had no proof to prove that he was drugged as all traces of the drug would have gone from his blood by the time she had prakash tested, and vidyut blackmailed her to marry him or else he would use the evidence to trap prakash and destroy neil and his family. Avni was badly trapped and didn't want neil having to arrest his own father on charges of murder when proving him innocent would be impossible too for neil, so she thought that the best way was to make especially vidyut believe she was dead so that his tricks against her, neil and his family would be of no use and he would leave them alone. The khanna's don't even know it was prakash who killed neela, and if they all knew the truth, they would not be mad at avni.