Trap Queen is slang for any loyal female that's down to ride and die for her man. This slang is mostly used by drug dealers to refer to lovers that put in work and can be trusted. A trap house
is a spot where drugs are exchanged/manufactured, hence the term Trap Queen.
Fetty Wap released a song titled "Trap Queen" in 2014 which became highly popular in 2015. In the song, Fetty Wap raps, "Married to the money, introduced her to my stove - Showed her how to whip it, now she remixin' for low - She my trap queen, let her hit the bando."
Fetty Wap - Trap Queen Video