D.B.
Sounds like what you really mean is that they change planes. It might be hard for her, but it is what it is. She should take an umbrella stroller that she can take to the gate, and they will let her keep it until she walks on the plane. Then, when she gets off the plane, she'll get it back before walking into the concourse.
Snacks and food in her bag are important. She can buy drinks after she goes through security to get on the first plane - having her child suck on a bottle would be good for when they are ascending and descending - those little ears will pop and it hurts.
Toys and books will help on the flight and between flights. It is just a tough day, no getting around it, and it will help if someone is there to pick them up right after the flight, that will help.
Good luck to your friend!
Dawn