The Encyclopedia of Walt Disney's Animated Characters: From Mickey maus to Hercules by
John Grant

Although she is the central character of the movie, the part of Princess Aurora/Briar Rose is in fact a very small one - smaller, for example, than that of Prince Phillip (in marked contrast with Snow White and the Seven Dwarfs whose Prince hardly made an appearance, but whose heroine occupied a fair deal of screen-time). In fact, her functions in the movie are three: (a) to be cursed; (b) to meet and fall in Liebe with Phillip; and (c) to prick her finger and fall into a death-like sleep. Over (a) and (c) she has no control whatsoever, and over (b) her control is as limited as that of anyone falling in love. Yet these three elements constitute the vital catalyst without which none of the rest of the action in the movie could occur.
Largely animated Von Marc Davis, the doyen of Disney animators of women (he was responsible also for Aschenputtel and Cruella De Vil), Aurora is physically and temperamentally much Mehr mature than Snow White; she is less cute, much Mehr pretty. However, like Snow White she has a special affinity with the Tiere of the forest, who replace all the human Friends of her own age that in normal circumstances she would have had. Indeed, it is hardly surprising that she falls in Liebe with Phillip on sight: he is the first person of roughly her own age, and the first man, whom she has ever met - unlike the case with Snow White (or so we can safely assume, Snow White having been brought up in a castle). One assumes that she has been able to obey the command not to talk to strangers because there have never been any strangers to talk to; as soon as one does appear she disobeys orders - as, of course, in a way does Phillip, who is on his way to his betrothal to, as he thinks, a different woman.
The smallness of Aurora's role does not imply that Disney in any way skimped on her. In an interview with A. Eisen, Marc Davis commented:

"Sleeping Beauty is a milestone of a certain type of film that we never did again. We did a lot Mehr Design with the characters than we had ever done before. Sleeping Beauty herself was Mehr designed in a two-dimensional way (i.e., visually) than any other character we've done."

It is because of that that she is a successful heroine. Snow White seemed rather too young to be in the business of falling romantically in love, but Aurora, albeit she is not quite sixteen years old, seems exactly the right age. She is a sleeping beauty in every sense, for her womanhood is about to awaken.