If you're looking for a Princess bonanza or just Cinderella in particular I highly recommend Akershus in Norway in EPCOT!
We've been there several times over the past few years for breakfast and we have always seen Cinderella there. Is it possible that we've just been lucky all these years ... sure, anything is possible ... but I highly doubt it.
HOWEVER ... if you look at the fine print for ANY Disney event, nothing is ever guaranteed. Disney, being the Empire that it is, KNOWS better than to guarantee anything ... you know what I mean, right?
Hope it helps! If you have ANY questions or concerns about this or anything else PLEASE do not hesitate to ask ... I'm at your disposal!
Like others have said she is definitely at Park Fare (not breakfast though) and she MAY be at PSB, never guaranteed. If you have to see her then I would do PF.