Ummm, by her family being an example for the world to see that "abstinence-only" sex-ed, which she supports, doesn't work.
If abstinence is followed, it most certainly does work and is the only fool-proof form of birth control out there.
So she chose to get preggers? I seriously doubt that. Come on, the politician parent stresses abstinence-only sex-ed and her kid gets pregnant. You don't see the irony in that? What if Bristol or her boyfriend happened to have a condom handy, don't you think there'd be one less pregnant minor in Alaska right now?
She chose to have unprotected sex. She knew the risks and took them anyways. Her choice, now she is dealing with the consequences. No I don't see irony in that. It was choices that she made, choices that were contrary to what she had been taught by her parents that put her in the situation she is in now.
If they had wanted them, they could have purchased condoms at any drug store. Again, they chose to not do so. They made irresponsible decisions.