From an interview with Neal Scanlan, head of creature and droid effects.
Interviewer: The original plan was to do Maz as a puppet. How far along did that get? And when was the decision made to go full CG or…?
Neal: Yeah. There was the truth of the matter was that Maz’s role in the film was always very fluid. As the scripts evolved, as J.J.’s ideas for Maz evolved, so did our technique. So the idea was at one time, Maz’s role was quite small. And at that time, that was perfect for a puppet. We could work in a very intimate environment with this character. We could deal with it in a very confined way. And as Maz’s role expanded, we looked at the possibility of doing it as a small person in a suit and having a sort of partial CG version. And but her role grew further than that. And at that time, we decided that to give the freedom to allow her to be developed in J.J.’s mind and also developed within the film, if we went to CG it would be a fabulous, that would be the by far the smartest move. Also as well, generally speaking, animatronic puppets and other things obviously don’t have the freedom a CG character has. And Maz was one character that needed a lot of freedom to be able to move around her own world. And for that reason, CG was chosen.