Janet is a redhead originally found at the Crimson Caravan Company. During the day she can be found tending to the brahmin and at night sleeping in the barracks. During breaks, she stares at Nellis Air Force Base through binoculars and watches a young man who stares at her as well.
Young Hearts: The Courier has to tell Janet that Jack is in love with her. After telling her she says she has the same feelings for him, but can't leave because she's under contract with the Crimson Caravan and can't leave without forfeiting her pay.
Sometimes Jack and Janet go to the non-accessible hill south of Black Mountain, and stand next to each other.
Sometimes Janet will be standing outside of North Vegas Square before the quest is given and thus be hard to find.
After completing Cass' quest Heartache by the Number with the violent solution (unless you Sneak kill Alice), Crimson Caravaneers become hostile and Janet is included in this. To bypass, use NCR affiliated armor and they should ignore you enough to complete the quest.
She may also get trapped inside a large rock at the outside of Nellis.