Tell her to download the BA app so that as soon as the plane lands, she can check which gate she'll need to get to whilst her plane is taxiing to the gate. I'm guessing she won't be experienced enough to whether her plane is parking at A, B or C, but that bit of time will help her formulate a plan. She can also download her boarding passes onto that, so there's no danger of losing any paper boarding passes (although always good to have those as back-ups in case her battery dies)