Is what happened with the questioner's sister—the rejection by the young man's parents—an affliction from Satan, and how should she be advised?

These matters are from the work of Satan and a result of impermissible mixing. Mixing in universities leads to forbidden relationships and infatuation that corrupt religion, mind, and body. Linking the acceptance of marriage to the color of a dress or the arrival of a person is closer to sorcery, whereas what is prescribed is performing Istikhara and relying on Allah. A girl blaming her Lord is more heinous than her blaming herself for becoming attached to a non-mahram (definition) young man. She should have a good opinion of her Lord, who knows what is best for her, and remember that "And perhaps you dislike a thing and it is good for you."