Just saw the beginning of the 5th video and a thought came into my head -
What if Shagun thinks she is dying because of these headaches, and she doesn't tell Sumer, and then arranges it so that Sumer will hate her and marry his child friend. Thus, she ensures Sumers's happiness.
Then she will find out that she is not really dying and his childhood friend was putting something in her food/drink to make her have the headaches and bribes the doctor to tell Shagun that she is dying.
I know this sounds far fetched, but the lying to save Sumer is something that Shagun has done before and might do again ...