Twi is an extreme overachiever and one of these days it's going to catch up to her. I understand her and how she puts herself under such pressure when everypony else wouldn't. Her friends were telling her to relax about it and I suspect Celestia would tell her the same...
"My most faithful student Twilight Sparkle,
I greatly appreciate the effort you go through each week to tell me what you have learned about friendship. What I notice, however, is that you greatly overreact about things you cannot control. My little pony, you do yourself a grave disservice and will someday end up in Ponyville Urgent Care if you do not relax. If you are late with a letter, I will not be in the least upset with you. I asked you to report your findings as they come, not by a certain date. Please, my dearest student, relax. I would not want to lose you too soon.
Princess Celestia."