Why has the result of repeated Istikhara concerning her marriage to a young man, towards whom she has developed feelings, not become clear, despite two years having passed and recurrent visions indicating her marriage is imminent? And is what is happening to her a trial, or a whisper from Satan?

Your question indicates your uprightness and your keenness for chastity. Your attachment to the young man may be a trial to elevate your ranks and expiate your sins. The dream may be a self-talk or glad tidings. There is no blame upon you in proposing marriage to him, directly or through an intermediary, while adhering to Islamic etiquette. However, inquire about him first regarding his religiosity and character. If he agrees, seek Allah’s guidance (perform Istikhara), and He will destine what is good for you. If the marriage does not materialize, turn your heart away from him, for Allah may grant you someone better than him.