Since Avantika saw that everybody including her own son was on Pankhu's side and wanted her to stay back, she came up with this shrewd plan to send of Pankhu packing on her own.
When Anuj, will ask for property Pankhu will on her won leave DM and go to show her Mahanta and save her Adi and her "Mom" from loosing property.
So Sanp bhi margaya and lathi bhi na tooti. Sheila was anyways against Pankhu, so she will be more than happy to help avantika in disposing of Pankhu and she can use it later to blackmail her, by spilling the beans to Adi and Nanu.
Please do let know your views and Avantika lovers please dont bash me. Nothing against her.