How do you "make sure"?
Do you have (or have you had) a teenage daughter?
If she has condoms in her purse the only way you know she uses them is to watch, although they are not fool proof.
If she has a prescription for birth control pills the only way to make sure she is taking them is to watch. But they aren't fool proof either are they?
Tell me EXACTLY how the Palins were to "make sure" she was on birth control. Tell me what they did not do right. How do you know she wasn't on birth control?
Ohhhhhhhhh ...you don't know do you!
Give her a shot of birth control that last for 6 months.
Have an IUD that last for 5 years.