Martin, seeing as he wasn't real flesh and blood, but in all intense and purposes was, didn't have a sense of danger or fear. Instead he was trying his best to tear in to Theo.
It only then occured to Morgan that Martin coming for her wasn't her worst fear. It was him coming for Theo and her family. Destroying everyone she loved. She had never felt terror like this before in her life. But seeing him slash and biting at Theo had her frozen in fear.
She knew Theo was strong, but so was Martin and Martin seemed set on inflicting as much damage as possible. "Martin stop!" She begged.