Well there are two ways in which
Disneyland accomodates guests with disabilities. By renting scooters and wheelchairs and also offerin what they call a Guest Assistance Card (GAC). You can get a GAC from guest services in the park (which I think is in Town Hall, any cm can direct you to where you get that). A GAC will allow someone to get the assistance they need to enjoy the park. For instance, some people can walk but they can't do stairs. So having a GAC that explains that will allow them to use an exit or entrance that has a ramp that might not be available to everyone. Your mom sounds like she needs a scooter rental and not necessarily a GAC. With a scooter or wheelchair, she can get on the ride either via the que (if its wide enough to accomodate a chair or scooter) or through the exit. The cm's at each ride que entrance can direct you as to how you get on the ride. Once you get up there and board the ride, they will hold the scooter at the loading area for you so its right there when you exit. You can also rent her a wheelchair, they are much cheaper but they get heavy to push all day long! Here is a link on general info about touring Disneyland with a disabiltiy that might be helpful to you:
http://www.disboards.com/showthread.php?t=1692922
Here is a link about the Guest Assistance Card, Go to post #6 for information on that. It is about WDW, but DL's GAC is basically the same:
http://www.disboards.com/showthread.php?t=595713
Cm's are always happy to assit you with questions once you are in the park.
My fil is diabetic and has a heart condition and we have done DL with him many times. We used to rent a scooter at the park (I think they are around $50 per day), now he has his own. You can rent a scooter at DL and take it over to DCA but you cannot take it to Downtown Disney. So if you want to see DTD, you might want to rent one from an outside agency. I don't know the names of any, but they are out there.
Have fun, your mom is lucky to have you take her to Disneyland! Its a lot of fun, and we were so thankful they had those scooters to rent so that my fil could enjoy the parks. Have a great trip!