This probably started as "community service" (by the decree of Her Majesty Princess Celestia, of course ), but then "Good Feels Good" happened and she agreed to stay in the position after serving her allotted time.
I love this image! In fact, it's inspired me to include this scene, or something like it, in my fan fic. I will not be useing your actual image, but there will be a scene where Trixie is teaching foals about stage craft.
As others have commented, it's nice to see Trixie happy.
Oh, how adorable! I just read a couple of fics with Trixie in them, and I had this very thought--she'd be great at getting little colts and fillies started in magic. (and as somebody noted down the page here, yes, she had had a few knocks, and gotten a nice slice of humble pie. hehe)