As I recall Bristol was asked when she told her mother she was doing the interview. She answered the day before. Greta announced since Bristol was 18 she did not have to have her mothers permission. Don't think Sarah had a say in the whole deal Just like Bristol deciding to have sex, mom didn't have a say in that decision after the fact.
The Bush daughters didn't get pregnant, but they sure partied and did plenty of embarrassing thing to the President.
Kids for better or worse make their own decisions.
What is more important to the future of America-that Bristol Palin was interviewed by Greta or that Sarah Palin called for Obama to veto the stimulus bill and thus forced him to take complete ownership of the bill? The former is a red herring, the latter-harpooning the big fish.