Dear Princess Celestia,
Applejack already told you what she learned about friendship, but I have something to add. Namely that sometimes your friends might try to ease your load by keeping things from you it can actually cause you more stress. Though in retrospect I'm not sure that's really a lesson in friendship exactly.
After Applejack's bath, I still can't believe she didn't notice how dirty she was, I got some additional readings from her. I'm not sure what the differences mean but they are utterly fascinating. I also thank you very much for the information on phoenixes, and especially their feathers. I have a fairly good idea what is going on with Fluttershy now, even if it is very odd to even think it. It would explain almost all her recent odd behavior, and her attachment to that feather. It's also very helpful to know that such information was indeed in the book she checked out. Thank you greatly.
Also, I cannot thank you enough for sending along Luna's correspondence, and forwarding my own. Her thoughts have been invaluable in my current research. I didn't really doubt Luna exactly, but I was still surprised you agreed so fully how much more skilled she is with magic. It seemed like there was no question about magic I could ask you could not answer. I guess nothing stays the same, does it?
Your faithful student, Twilight Sparkle