I think SnackyStacky meant what was written in a different way than you understood.
Most lines are wheelchair and/or
ECV accessible. For the lines that are not accessible and require a different way to access or board the attraction, some people have invisible needs to use the accessible boarding area. For example, someone with knee or hip problems who is not using an ECV or wheelchair might need to board at an area that avoids stairs (like at Toy Story Mania) or at an area where the moving walkway can be stopped or slowed. CMs would have no way to know about those needs just by looking and those people would need to have a GAC.
Someone like your friend has an invisible need to use the ECV, but the ECV is visible, so the CMs would know that she needs to use whatever is the accessible entrance. She would not need to have a GAC to do that since the CMs can see that she is using an ECV.
If using the ECV in line was not enough and she had
additional invisible needs (for example, radiation damage that means she needs to avoid sun), then she would need a GAC for the attractions where that would be a problem.
But, most people using wheelchairs and
ECVs don't need a GAC.
For people who want more information about GACs (Guest Assistance Cards), click on the link to the disABILITIES FAQs thread in my signature. Post #6 of that thread is FAQs about GACs.