Hi Amanda,
Thanks for visiting the Disney Parks Moms Panel with your question.
I would hate for your princess to be disappointed, and I don't think she will be. I have looked all over the official Walt Disney World website and I've checked all the unofficial sites that monitor events such as attraction closures, and I can't find anything to indicate that the
meet-and-greet area with Ariel will be closed this month.
In fact, the Magic Kingdom calendar right now shows that Ariel will be greeting guests in her grotto in New Fantasyland from 9 a.m. to 10 p.m. on Sept. 14, the day you plan to visit. I don't see times listed for the rest of the year beyond Sept. 14, but my best guess is that the schedule just hasn't been loaded into the calendar yet. I hope that's the case.
When you arrive at the Walt Disney World resort, you will get a Times Guide that lists the most up-to-date character greeting information and any attraction closures. That will be your most definitive guide.
Good luck! I'll keep my fingers crossed for your daughter.
Wilma