The reason this is a problem is not because the daughter is pregnant. In terms of her being VP (or POTUS if necessary), its a minor issue. The problem is that one of two things is true. Either she did not tell them when she was being vetted, which is a shame on her kind of thing. Or, she did tell them and the decision to tag her as VP is highly suspect.
According to reports, a McCain adviser claims that they were told. Well, of course they are going to say that because if they say she didn't they sound like they are blaming her. I don't believe it because if that were the case then when they announced her as the pick the McCain camp would have reported that themselves to minimize criticism.
Seems to me most likely scenario is she did not tell them, they did not find out until afterwards, and now she is going to quietly find an exit.
Have to say overall this is poor commentary on McCain's staff. If I'm McCain, I'm freakin' furious.