Would this act of mine, photographing a girl who asked me to do so in a bad light, be considered under the ruling of zina (unlawful sexual intercourse)?

You have done well by protecting yourself from the aforementioned forbidden acts, but you have done poorly by establishing a friendship and communication with the girl; thus, you have opened the door to evil for yourself. You have committed a series of sins, leading you from minor to major, and one sin calls another. Repent to Allah and cut off your relationship with the girl. Be keen on everything that helps you remain steadfast, just as Allah warned against following the footsteps of Satan in His saying: "O YOU WHO HAVE BELIEVED, DO NOT FOLLOW THE FOOTSTEPS OF SATAN. AND WHOEVER FOLLOWS THE FOOTSTEPS OF SATAN - INDEED, HE ENJOINS IMMORALITY AND UNLAWFULNESS. AND IF NOT FOR THE FAVOR OF ALLAH UPON YOU AND HIS MERCY, NOT ONE OF YOU WOULD HAVE EVER BEEN PURE; BUT ALLAH [PURIFIES]..."