Is the girl wrong for staying at home after performing Salat al-Istikhara and refusing to work, and is the death of her fiancé two months before the wedding a punishment from Allah for disobeying her parents by not working?

Your decision to leave your job was correct if you were not in need of it or if you found religious prohibitions in it, as this is more befitting for a woman. However, if there are no religious impediments to the work, Islam does not prohibit a woman from working, provided it adheres to the religious guidelines. Your performance of Istikhara (seeking guidance from Allah) is the Sunnah, based on the Prophet's (peace be upon him) saying: "If any of you is concerned about a matter, he should pray two rak'ahs other than the obligatory prayer and then say: 'O Allah, I seek Your guidance by Your knowledge...'" (the rest of the hadith). Whoever does that, Allah Almighty will not abandon them. So, be patient and seek your reward from Allah Almighty, and say: "It is the decree of Allah, and what He wills, He does."