That was exactly my problem (see also reviews of self). I have no problem buying this kind of behaviour from 19 years old Rose in Father's Day; she's young enough, has enough Daddy issues and is new enough to the whole time travel business. But Sarah Jane, between 50 and 60? Who otherwise doesn't just have the experience and the willpower to know better, but would never be so ciminally irresponsible and selfish to even after she's seen the apocalyptic alt!Earth say she can't let her parents die? *shakes head*