Now see, that is what I thought! But I am a librarian and a patron I spoke to this morning said she just got back from a holiday trip to Disney and they asked her for a letter??!! I didn't think they could do that! We didn't need one in 2006.
They can't do.
The ADA (American with Disabilities Act) says that proof a disability can't be required in order to provide accomodation for a disability.
Some people do feel better about asking for a GAC if they do have a letter from the doctor, especially for invisible disabilities. It is your choice of whether or not you bring one.
And, as some people posted, many people have posted in the past that they wrote a little reminder sheet for themselves and either read it or handed it to the CM to read.
It's probably that she had a letter and handed it over to them. Because they took it, she assumed that she needed it. People sometimes get their wires crossed. They definitely shouldn't ask you for a letter, and if they do, politely ask to speak to the manager, and straighten things out with him or her.
I'm sure that happens.
If you choose to take a letter, OMHO, it should specifically state what the problems/needs are. The diagnosis is not important, partly because the CMs don't need that, partly because the CMs are not medical people and may not know what the diagnoses mean and partly because different people with the same diagnosis can have very different needs.
I know that formats stating the diagnosis and asking for "any available accomodations" have been on different internet sites as a 'suggested letter format' to request a GAC.
The problem with the format is that it really doesn't tell what the person needs; "any accomodations" doesn't really give the CMs much assistance in figuring out the needs. I have been in Guest Relations when the CM has been trying to question someone on what might be helpful/what the needs were. The parents were getting frustrated and just kept saying "we HAVE a letter from the doctor. We need what he wrote." The CM was getting frustrated because she needed some guidance from them on what the child's problems were so she could figure out what accomodations would be helpful.
I have heard the same conversation quite a few times and CMs have written me to tell me how frustrating it is for them. They want to help, but don't have enough information to be helpful.
So, my suggestion is if you want to bring a doctor's note, make sure it talks about the specific needs the person has, not just the diagnosis and blanket statements.