How does a girl become horny?

To get yoursel horny poke yourself a little and then rub your breasts or even kid on your someone else feeling you up then addventually youl get horney x:)
Tease yourself by denied temptations and hidden "naughtiness" over extended periods until relief becomes essential. Be aware however that your growing sexual tension may become recognisable to others. Either avoid public places or feed off public attention, but avoid crossing any legal limits. Acceptible behaviours and turn-ons are different for males and females, older and younger people, and legal issues vary for each and in different jurisdictions.

e.g. At home in private, set the environment, temperature slightly hitter than usual, dim lighting, scented candles, soft music, arousing images, sexual sounds such as "Mood Effects" ((sounds of people in a groups sex scene on CD). Then dress for the occasion, sexy or semi-nude, scantily dressed, without underwear etc depending on whether you're likely to be disturbed. Hot shower or bath, sensual soaps, oils, toys any lubes. Gotta go now, bye!