This story is a sequel to Fallout: Equestria - Pip and Tia

Heart's Warming season comes to the post Wasteland, a season of remembering one's true love ones and taking joy in what one has. But every pony has such joy, one mare seeks a loved one that was ripped away from her years ago. Hanging onto to hope she will them the mare pleads to Pip and Tia to help. Will her Heart's Warming wish come true or will they fall on deaf ears?

This is part of the Pip and Tia series but is a self contain a story, no further reading is required. But here is the rest of the series.
Fallout: Equestria - Pip and Tia
Fallout Equestria Pip and Tia: Divine judgment

Edit: this is just a One off. Also Derpy's my current player character in a Modded run im doing of Fallout New Vegas currently.

Derpys past was a mystery to some. There were a few that thought she was a Ghoul from the prewar era. Others simply didnt want to cross her as she had been called a Spirit of Vengeance. She was a package delivery mare, but that didnt mean she didnt know how to handle herself when the time was right. She was the one mare that you never wanted to cross when she was determined.

You can just call her Courier Six.