It’s hard, but it CAN be done! If she gets really focused, you could try thwacking her (gently!) on the ribs with the doubled-up end of the leash; it makes a loud noise, and is a form of contact most dogs are not familiar with, but you can’t really hurt them with it; it’s usually enough to startle them out whatever obsessive zone they’ve gone into.
Yesterday she saw a cat just at the point that my 15 year old let go of her collar and ran out of the yard, as he ran after her. She jumped into the neighbor’s yard and my son yelled, “Hold!” She listened. When they came back in, I was torn between “bad dog” because she ran and “good dog” because she stopped on command.