Mistaken Identity

Why is Astryd of Baalfire so willing to believe that Vinny Balfour, from the 21st century is her missing son, Vincent?  They may have a striking resemblance to each other, a family connection passing across hundreds of years, genes handed down from one generation to the next.  But a mother knows her son.  Reasons are hinted at in the short story (free this weekend) The Bullying of Harald Ruffsnape.  Of course, there's more evidence to be found in The Dragonscale Blade.  Perhaps she knows more than she is prepared to believe.  If she were to face up to the facts of her son's disappearance, life might be unbearable.