The trouble with having no access to a vice-presidential candidate is that you have to parse edited statements like Kremlinologists. The record is very clear that the decision to accept the veep nomination was kept from the Palin children until they arrived in Ohio on what they were told was a surprise trip for their parents' wedding anniversary. Here's a Fox-approved Kremlin interview with Todd Palin that re-confirms the official tick-tock provided by the McCain campaign. It's clear from this that the girls did not vote after McCain had offered Palin the job. But they may have been asked long before that about the possibility. The only trouble with that explanation is the way Palin put it in her Hannity interview. She said:
"It was a time of asking the girls to vote on it, anyway. And they voted unanimously, yes. Didn't bother asking my son because, you know, he's going to be off doing his thing anyway, so he wouldn't be so impacted by, at least, the campaign period here. So ask the girls what they thought and they're like, absolutely. Let's do this, mom."
This strongly implies that Palin had already been asked and was offering the girls a vote on the question. "Let's do this, mom," is not a response to a hypothetical. It certainly reads like an enthusiastic response to a choice on the table. Without the context of what "it was a time" is referring to, we can't know. I guess we'll find out eventually, although we haven't about almost anything else.