grits,
If the GC girls are still playing hard there are a number of things that you can do where both teams can still benefit.
At 4-0, 5-0 or 6-0 (choose one)....start the restrictions.
Limit JI's touches to 2 or 3 and only allow goals to be scored on headers off crosses. The score will not exceed 10-0 and you will often lose possession to GC, forcing both teams to "hustle" and the game will appear competitive. Both teams will get something out of this and JI will not be accused of humiliating a team that works their butt off and deserves better.