Is it permissible to rely on a dream after performing Istikhara to reject a religious and well-mannered suitor, and is it necessary to see a dream after Istikhara?

If it becomes clear to the woman that the suitor is a man of religion and good character, and she has sought guidance from Allah (performed Istikhara), then she should agree to marry him. The result of Istikhara is either the facilitation of the matter or its diversion, and it is not necessarily the seeing of a dream, as dreams can sometimes be mere self-talk.