Robyn,
Typically you will get to see Cinderella and her Fairy Godmother at
Cinderella's Royal Table for breakfast. Now they also state on the website that her "Royal Friends" are there to. What this means is that there can often be another princess (and suitor) in attendance, but whom that might be changes frequently. I have seen both Ariel and Belle there (at different times), but there are no promises.
While this is a special experience, I prefer the meals at
Restaurant Akershus. There are always more princess in total there, though Cinderella may not be one of them. My girls like ALL the princesses, so they are not headed to see Cinderella specifically. So they will get all gaga about who they see, not who they
don't see there. Oh, and it is less expensive at Akershus.
So if it has to be Cinderella, then go to the Royal Table. If it just about princesses in general, then I recommend Akershus.
I am glad to answer any follow-up questions!
Have a magical (and delicious) vacation!