What is the ruling of the Sharia regarding my exposing a girl by publishing her private photos to her managers and colleagues at work? And is this considered defamation (tashheer) or slander (qadhf)? And how can I be saved from the wrath of Allah? And do I have legal obligations towards the girl for my repentance to be accepted?

Your action resulted in the widespread circulation of indecencies among Muslims, tempting those to whom you sent the pictures and exposing them to unlawful gazes. This is because if the soul is far from indecencies, it is oblivious to them. However, if it finds someone who reminds it of them, the latent temptations are stirred. Ibn Ashour explained that a believer only wishes for his brother what he wishes for himself. Thus, he does not like evil rumors to be spread about him, nor does he like evil to be spread about his brothers. This is because the spread of indecencies among believers causes moral corruption and diverts their thoughts from hating its bad reputation. If talk of an indecency spreads, thoughts recall it, and leniency towards committing it creeps into souls. This act is a major sin, but it is not considered slander that necessitates a prescribed punishment (hadd). You must repent to Allah, pray for the girl, and seek forgiveness for her. Beware of contacting her or approaching her.