After the muffinman, now we have the Element of Muffin.
Beautiful and adorable work
She would deserve to be the keeper of an element
You did a great job here especially at her dress. It includes all the details which represent her (like the bubbles from her cutie mark).
I actually think if there would be seven elements of harmony Derpy could be the seven and I'm pretty sure it would be the element of "charity". Or even (as you said) the element of MUFFINS