I've been to two different auditions before:
The first was for a "character" when I did the college program. In this audition, they did have you do a dance and an animation as described previously. They called a few people back in to audtion for "face" characters (one of the girls in my group just said they had her try on a wig for alice).
However, the second, which sounds more like the one your sister is going for, was in Orlando at the AK facility. At this one, you signed in, waited in a *long* line (as previously posted, do get there early, so you don't have to wait forever - we were about 15 minutes early and still had to wait about 3 hours). They will weigh your sister and get her height with her shoes off. Again, as others have posted each character has a determined size they go for. After this, they moved us into a room in groups of about 40-50 people. Once in there, the lady described how not to be discouraged, they have a specific thing in mind, and while you might have perfect features in general - that each character has a certain look and you have to fit that to get it. They had us in about 4 lines, and they looked at the front row face on, and then in profile, and then the next row moved up, etc. After that, the lady (and a few others in the room) took a few minutes to talk amoungst themselves, and then out of the room of 40-50 people, at least at my audition, they only called one name to move on. I'm not sure if that person had to have an additional audition, or if he automatically got the spot from there, but that's how my experience went. Make sure to tell your sister good luck, and tell her not to be discouraged if she doesn't make it. They are really really tough roles to get - disney looks for their own kind of perfection there.
Anyway, I am excited for your sister and am living vicariously through your experience. 
