Unfortunately your terrier will be inclined to scrap if your holding the lead taught...when a mutt is approaching why exactly are you holding the lead so taught.....if it's out of range why indicate to your terrier that trouble is imminent.
unfortunatly on,off,taught,loose she will scrap!!this saves me falling out with people, that think every dog needs to sniff every other dogs arse!!!!!!!!!!!!!and when people have been told not to bring there dogs to mine,and still choose to do so there isnt much i can do apart from hold her back!
She wont scrap if you grab her collar and spin her