I am not sure. A quote from an article by the EAZA Elephant TAG:
"This effect is already very much apparent in the Asian elephant EEP and led to the decision to deliberately reduce birth rates by aiming for eight years as the first age of reproduction for females, a last age of reproduction of 25 years and an interbirth interval of seven years."
Source: EAZA Zooquaria #117
I guess this is the general rule with exceptions. Zoo Zurich reports on their website that Panang shall have offspring with Thai. I also have my doubts that this succeeds, but the general situation is that there are about 30 matrilines in zoos = 30 potential future breeders in Europe. Losing any of them will hurt in the future, so I can very well imagine that they do exceptions in situations, in which a cow is desperately needed to keep the line alive. Personally I think it would be better if Zurich sends the other matriline away though, given the recent past and the fact that the two groups don't get along with another...