Sending her away was against the EEP guidelines and keeping all these breeding age females permanently without a bull too, but since the elephants are owned by the Twycross Zoo, the EEP can`t do anything against it. They could kick them out of the EEP and the EAZA, but such drastic actions are very, very rare.
Yes that's part of the problem. Twycross are in effect free to continue managing their elephants in whatever way they choose. The two cows being sent to Chester for mating was probably a one -off (similarly they once sent two non-breeding gorillas away on breeding loan but didn't repeat that either)
I wonder what will happen if any of their other elephants become 'difficult' like Karishma ... Presumably Whipsnade have the facilities (protected contact?) to control her behaviour.