border collie

Question
I have a border collie bitch, who is very obedient, knows all basic commands ie sit down stay etc. She loves  to herd dogs and comes back when called. The other dogs are dogs she knows and this does not cause a problem to me or the other dogs and their owners. It is a brilliant way to exercise her. Only problem is when one particular dog appears (a Springer Spaniel she knows). She will totally ignore me and run from one side of the park to the other to chase and herd this dog. I shout,blow the whistle, which any other time works, but to no avail. The only way is to get closer and eventually get her to come.She also does this with rabbits, so I cant take her for country walks, which is  a shame. I would be very grateful.a shame.Please if you have any ideas I would be very grateful. I have tried sweets, balls etc, she is not interested.

Answer
It appears there is no positive reward you can offer that will compete with the joy she gets from herding the Spaniel and chasing rabbits. You could quickly regain her attention and have her do a reliable recall regardless of distractions with a shock collar. That would cure the problem. Many dog owners are adverse to shock collars and refuse to use them under any circumstances. I respect their opinions. However, as a solution to the issue you raise, a shock collar would be the most efficient and possibly the only method of achieving your goals.