As long as hew bags are checked through to her final destination, and she has a boarding card for her T5 flight (although this can be collected at T3), she can connect to T5 airside. This is assuming that her T5 flight is international and not domestic, otherwise she will need to pass through immigration.

Tell her to follow the purple signs to flight connections for T5. She'll need to re-clear security though.

Hope she has a good trip.