The Girl Hitchhiking is a minor character in Grand Theft Auto V, that appears in the random event Hitch Lift 3.
Background
Not much is know about the girl's life. She says during the ride that she was having a party with some friends in Sandy Shores, in the night prior to her random event, and that she doesn't even remember going to bed. She has an unnamed boyfriend whom she rarely sees, only visiting him to get more money once she's run out. She describes herself as a sexy, bohemian girl that goes out for days and takes ecstasy in the desert. She justifies her style of life, saying that she is still young and just wants to explore her mind and discover who she is.
The girl seems to only maintain a relationship with her boyfriend for his money, as she says during the ride that she spent all the money that he gave to her and gets nervous when the protagonist accuses her of only coming back to him when she runs out of money.
Events of GTA V
The girl can be found at the junction of East Joshua Road and Route 1 in San Chianski Mountain Range, she asks the protagonist to take her to Mount Haan Drive in Vinewood Hills.
This can't be completed with Trevor Philips or Michael De Santa during their exile, as traveling into Los Santos will trigger Martin Madrazo's men to come after them which will freak her out, failing the random event. It is possible to take her to the Altruist Cult if playing as Trevor at any time.
She says that she is going to meet her boyfriend, that works as a security guard in the broadcast tower behind the Vinewood Sign, to pay him a surprise visit.
Along the way, her boyfriend calls her and gets very angry when she says that a man is giving her a ride back to the city as she has exhausted the $1,000 he had loaned her. The girl even asks the protagonist to say to her boyfriend that he is "just a random guy not called Brian", just to calm him. After this, she gets a second call, this time she talks about the party in Sandy Shores and it gets pretty clear that she is talking with Brian, the man that her boyfriend was so jealous about, when the protagonist confronts her about this, the girl lies saying that it was not Brian, just one of her friends.
When they get to the destination, her boyfriend confronts the protagonist asking if he is Brian and starts a fist fight with him. If the player pulls out a gun to threaten/kill her boyfriend, she will run away and the random event will fail. The player then will need to wait some time to try her random event again.
When the protagonist knocks him out, the girl gets upset and calls the protagonist a psychopath. She can then be allowed to stay with her boyfriend or she can be killed. Either way, she will not appear in the game again.