Twilight: Derpy. You are not a failure or a featherbrain. I can tell deep down that you are a very kind and intelligent pony. Trust me, Derpy. Most ponies out there donít look at you for who you are. They see what they feel like seeing and then go on with the rest of their lives, oblivious to what hurt they may be causing. You need to look past that, because the ponies who donít take the time to care, donít deserve the satisfaction of making your life miserable.
Derpy: How can you possibly...
Twilight: ...Know that? I know that because up until two years ago that was an exact description of me as well. Before I moved to Ponyville, I had one friend Ė Spike Ė and I barely treated him as a friend, more like just a helper. I didnít understand the effects that friendships can have on ponies or how much they can infinitely change your life for the better. I think that this may be your first hurdle to a happy life, when you realize that your life is what you make of it, not what others tell you it is. You need to start with finding a true friend, a friend who will share in your joys, sorrows, pains, and help lift you through the difficult times when they come.
Derpy: Twilight, youíve seen what a mess I make of everything. Youíve seen the looks ponies give me. Where am I supposed to find a true friend when I canít even find a pony that will put up with me for more than a day?
Twilight: WellÖ ever since I came to Ponyville, Iíve made many friends, and Iím sure you know that Applejack, Fluttershy, Rainbow Dash, Rarity, and Pinkie Pie mean the world to me. I donít think that there is a limit on the number of truly dear friends I can have, so... Iíd be glad to have you as a close friend, too.
When Twilight offers to take Derpy on a tour of Ponyville to prepare for her new job, Derpy is reluctant, as she doesn't want to risk damaging Twilight's reputation by being seen with her.
Twilight: Derpy, listen to me, and donít ever let yourself forget what Iím about to say. I donít want you to think, ever, not even for a moment, that I would be embarrassed by you. If I was that concerned about my image that Iíd avoid being seen with you, then I wouldnít be your friend in any sense of the word. I meant every word that I said to you, Derpy. You are my friend. I am not going to throw away something so important because some random judgmental ponies out there think itís strange that I like you.
Post Haste, the head of the Ponyville postal service, gets one in just about all of his interactions with Derpy:
In Chapter 4, he praises her performance on her first shift in Ponyville and offers her the job that the Cloudsdale office just fired her from (over an accident that wasn't her fault).
In Chapter 5, Derpy tries to pre-emptively apologise for the mistakes she's likely to cause. He makes it clear to her that unlike Crafty Crate, he will support his employees through anything, and that she's an outstanding mailpony who should not doubt herself.
In Chapter 20, he rewards her performance by offering an extension to her route - specifically, Fluttershy's cottage - and correcting her unjustly low place in the pay scale from Cloudsdale, resulting in a 35% raise.
Never before would she have imagined that she would be commended for her ability, given more responsibility, and rewarded with a substantial raise. She couldnít comprehend even getting one of those results, but having all three happen simultaneously left her utterly speechless.
Derpy: IÖ I donít know what to say. ďI canít even begin to describe what this means to me. Iíve never been rewarded like this for anything before. I just hope I donít let you down. Iíll do my best to meet your expectations.
Post: Iím sure youíll meet them and more, Derpy. Youíve exceeded my expectations more than you know, and, to be honest, youíre the most dedicated mailpony Iíve ever hired. You deserve recognition for that Ė Iím just sorry that it took so long for you to receive it.
In Chapter 16, Rainbow Dash resolves to let go of her long-standing grudge against Derpy upon realising that she's basically what Fluttershy would have been had she not had Rainbow Dash for support. The following chapter has a particularly moving apology from her:
Rainbow Dash: Iím sorry for everything that Iíve ever done to you, since the day I first met you. I never gave you a chance, I never got to know you, I just joined in the crowd making fun of you, and itís only gotten worse since. You never deserved any of it, and if I had only stood up for you, your life may have been so much happier. Thatís why Iím sorry, and why Iím asking for your forgiveness. Iím apologizing for years of undeserved misery for you that Iíve been an eager part of.
After some hesitation, Derpy hugs her.
Derpy: Rainbow Dash, I accept your apology, and I forgive everything youíve done. Itís not easy for me to forget the past, but the past does not need to be forgotten to be accepted, and it does not need to be ignored for us to move on.
While Celestia's letter to Twilight in Chapter 24 ends on very bad news, she warmly congratulates Twilight on her newfound love and makes it clear that she takes no pleasure in forbidding her to use the exotropia spell again.
Twilight and Derpy's reconciliation after the former tore up the library when her magic got out of control due to her anger at Celestia and almost injured the latter.
From the same chapter, Derpy reveals that she's come to accept herself for who she is, at which point the last of her Cutie Mark bubbles changes colour, to grey with a blonde edge.
Derpy: Itís not a big deal. In fact, it doesnít matter at all Ė Iíve never been happier than I have been after meeting all of you, regardless of what my eyes have been like. I donít need my eyes to get better. I just need you girls for friends.
The epilogue. Twilight and Derpy have gotten engaged.