How many of them are there? Is she flying with kids, and how old?
If she has kids who would need a car seat or booster and they don't want to bring them, I'd recommend the Disneyland Express. We took it when our DD was nearly 3, and it was fine (and we loved not lugging the car seat with us). Otherwise, probably Super Shuttle.
The Disneyland Resort Express is okay, but with more people a private shuttle like Zippy, 4Most Coach or Karmel is better than a shared service like SuperShuttle.