What is the interpretation of the dream a girl had after performing the Istikhara prayer, in which she felt comfort at times and fear at other times, regarding the young man who proposed to her?

You have done well in performing Istikhara (seeking guidance from Allah) and consulting others, and a Muslim should be diligent in both in all their affairs. As for the dream, it has no relation to Istikhara, and nothing should be built upon it. If it is a good dream, it is from Allah, and if it is otherwise, it is from Satan. Its beholder should seek refuge in Allah and spit to their left if they fear it.