Stealth Girl

Stealth Girl is a perk in Fallout: New Vegas given by Lily if she is your companion. You may obtain Lily as a companion during the Guess Who I Saw Today quest.

Effects
With this perk, Stealth Boys last twice as long while also granting sneak attack criticals an extra 10% damage. This perk makes a single Stealth Boy last for 4 minutes (instead of 2), this has a great synergy with its other effect, increasing sneak attack damage. Any sneak-based character would benefit greatly from the perk.

Behind the scenes
This perk is named after the Stealth Girl, an item in the canceled Fallout: Brotherhood of Steel 2. The Stealth Girl acted as a Stealth Boy, but lasted three times as long.