My mom is disabled and has a lot of physical issues, but if you looked at her you wouldn't really notice it unless you knew her or watched her face. I keep telling her she needs to get a GAC because it is hard for her to stand for long periods of time, but she's afraid a cast member will turn her away or people will make fun of her. Is this something that happens often?

Trust me, a lot of people are the same way so your mom is not alone. In recent years CMs at all the US parks have been dealing with a lot of people abusing the system, claiming they have an disability when they just want to skip the lines, This is INFURIATING because we know that there are people like your mom out there who really need accommodations. Let me tell you that Cast Members should NEVER deny your mom use of the system just because she doesn’t “look” like she has a disability (and if they do please report that scum immediately). We’re using a different system now for disability access similar to Fastpass, and Guest Relations and the Cast at attractions will be able to help you out. Don’t be afraid to use it if your mom needs it!