Caution: this is a report on a mod that has slight connections to a Metal Gear Solid V: Spoiler. The spoiler will not be revealed or discussed, but keep in mind that it addresses it.
Quiet is one of the companion characters for Venom Snake in Metal Gear Solid V: The Phantom Pain. There is a point in the game where Quiet is unavailable to be selected as a buddy. However, a mod shared by WASDREF makes it possible to bring her along in the Windows PC version of the game, even when it shouldn’t be possible.
The Metal Gear Solid V: The Phantom Pain mod is 52.2MB in size, and WASDREF recommends making a backup of your save file before using it. After Mission 43 is completed, a player can take the Data1.DATA file from the .zip file and drag and drop it into C:/Program Files/Steam/Steammapps/Common/MGS_TPP/Master to install it in the game. (Note: The location of your Steam folder may be different than mine. Wherever you installed Steam is where you want to go.)
Once installed, load Metal Gear Solid V: The Phantom Pain. Quiet will be available as a buddy for Venom Snake.