Parvati knew that Padma hadn't been privy to everything that the DA was doing as it was. To some extent, Parvati wasn't sure that everyone had been telling her everything either - she had the sneaking suspicion that the night that Padma and Seamus had gotten locked in the greenhouses it was part of a larger DA plot that neither of the Patils had been let in on. She'd never asked because she hadn't wanted to know and have to decide between her sister or the DA.
"It might make sense," she said slowly. "It's hard enough for me just being a prefect and staying involved, I can't imagine what it's like for you and Ernie as Heads. And nobody wants Pansy as Head Girl."