I would tell her the best indication of future behavior is past behavior.
He disrespected her and broke up,going back to him will most likely produce more of the same.
They are casual friends and since they are not bickering,it would be acceptable to say hi if they meet on the street.
He gave her no encouragement after the fathers day greeting and that indicates that he has moved on,she needs to do the same.
You can't make someone want to be with you.