Her wording on whether abstinence education prevents teen pregnancy is circuitous:
While there is a role for abstinence education in reducing pregnancies, studies have shown that often it is not enough. Many children who have been told to just say no end up having sex, anyway, but aren't equipped to prevent pregnancy because they often don't plan to have sexual intercourse. A combination of abstinence programs with comprehensive sex education focusing on safe sex and pregnancy prevention is thought to be a more effective way to deal with preteens and teenagers.
As written, the first sentence sounds like abstinence education works sometimes, rather than not at all (as far as we know). The second sentence is pure speculation. And her description of sex education makes the abstinence portion stand out, perhaps in an effort not to alienate readers.
To be honest, very few program evaluations measure teen pregnancy because it's usually rare in the general population (her readers). Sex ed is much more effective in getting kids to delay sex and use condoms more (or at least claim to). Pregnancy is hard to affect using just a curriculum. Perhaps unsurprisingly: there are always kids who don't pay attention to any curriculum in any class, and they may be the same ones who get pregnant.