I was actually going to make a topic about Sofia the First when I noticed this one.
I have only just started watching the series, so I can`t answer your question, but just wanted to state my opinion on the series in general. So far, I`ve seen the pilot movie and 8 episodes, and I`m quite enjoying it. It`s got good lessons and morals, a likeable main character and I love the concept of a child coming into a royal family as a step-daughter/sister. Very refreshing and interesting.
There have been no Disney Princesses appearing so far, except for Cinderella in the pilot movie, so hoping to see more soon.
When I first decided to give it a chance, I had fairly low expectations and considered the show suitable for small children only, but I was pleasantly surprised! It`s fairly smart and blessedly low on dumb gags. If you`re a princess fan, I`d say give it a go!