My mom is travelling IAD-FRA-MAA on LH on Aug 6-7 and then MAA-FRA-YYZ on Aug 19. I've researched excessively online but would really appreciate help for the following questions. She's not handicapped or disabled but because of her age, she can walk long distances only quite slowly. Thankfully connection time is not an issue as she has >5 hours in FRA each way.

1) From what I can tell, IAD-FRA will likely arrive in Z and FRA-MAA will likely depart from C. Can she walk the connection or will she have to take the SkyLine train? And I assume she'll need to re-clear security? My understanding is it's still quite a walk from the BC Skyline stop to the C13-16 gates where the MAA flight usually departs from.

2) From what I can tell, MAA-FRA will likely arrive in C and FRA-YYZ will likely depart from B. Is C->B a walking connection and will she need to re-clear security?

3) I saw mention on the FRA airport guide on the sleepinginairports website that "If you need to go a long distance in a hurry, look for one of the blue-and-white Terminal Express cars that serve the entire transit zone. You can ride them free of charge." I've had difficulty locating further info about these online. Are they only if you've requested mobility assistance with the airline, or can anyone use them? Does anyone have further details on how it works?