Runjhun should herself learn a lesson fron this and never trust her M&Ms again. She should at least be able to understand that the motive behind this food incident was to drive a wedge between her and Guddu. She should lookout for herself and Guddu.
And I think Guddu will believe Runjhun that it was not her fault. He also should use his big brain and deduce that M&Ms are the real culprits and not Runjhun.