Never count out a guerrilla force willing to fight and die for their homes.
There was no home left to fight for. And for much of her campaign of crazy, she only had one battlestar.
Her duty was pretty clear - she'd found some remnant of the human race. Take them and run and keep running and run some more. To be fair Adama was going to fight at first, as well, but at least he was willing to listen to a voice of reason. And he wasn't plundering the civillians for parts.