“Why does AJ get to use the potty!”
 
“Well, considerin the look of yer diaper, I’d reckon you’re not ready just yet dashie”
 
“hmph!”
 
“now now Dashie, you don’t need to worry, you’ll be ready for potty training eventually. Now come over here and I’ll get you changed~”
 
Seems Dashie has gotten the short end of the stick in this situation and is still i diapers, well hopefully Applejack gets her comeuppance for picking on poor little Dashie.
 
First: Here 
Second:  
Third: Not Yet 
Fourth: Not Yet