Most, if not all, Budget airlines do not allow food not bought in flight. This is a income source for the airline. The other main reason being food may have smell that others find pungent, just like that curry rice the lady is eating in flight. Such smell takes along time to get rid of.
She should be told to junk that food, or throw off the flight, even if it already in flight. All passengers should demand a refund as this is a clear breach of flight condition clearly stated in the ticket purchase T&C.