Had the sword spirit of Jacob's Dragon Slayer's Sword not been damaged, he wouldn't have needed to intervene at all; Sofia could have easily knocked the old woman back on her own. After all, Sofia's strength increases proportionately with the Dragon Slayer's Sword. As Jacob grew stronger, the Power of Dragons helped fortify the sword as well.
However, since Sofia was wounded and could not leave the Dragon Slayer's Sword, Jacob had to go to the Divine Forging Sect and treat the sword at the sword-cleansing lake to heal her. Once healed, Sofia's power would increase tremendously upon leaving the sword.