Move forward a bit until 2 manhacks swing into the room. She’ll cover this side of the train station.
When you walk out, Alyx should take up a position by the machine gun. You do get a revolver and a fair bit of ammo though, so we can’t complain too much. Once you get the first group over, the attack will begin and they’ll make the genius observation that they should have had them all go at once. We need to be able to get new supplies quickly and heal on the go. Go slowly and take note of all the locations. Once we get through this office area, the refugees will take cover by the trains. There’s another dispenser here and a machine gun position by the exit. You need to go down the ramps and around the trains.