I must say that I'm a little surprised over the notion that the politics of the social democrats would be wrong. They had invested in a coalition with the Greens which seemed very good at the time. After all, the Social Democrats were in the lead in the polls all the way to the spring.
However, after the Copenhagen meeting, when China and the US killed off global concern over climate change, the interest in the the Red-Green alliance faded. Mona Sahlin had originally not included the Left party in this alliance which in retrospect was probably quite prescient.
I have not seen the fact that Mona Sahlin was unpopular in her own party as the reason for the change. It is of course very difficult to win an election when your coalition partner is more popular. After all, if the party believed in the Green bent they should follow up on this. The Moderates seem to believe in this continuation since they brought in a greenish party secretary, Sofia Arkelsten. Also, Fredrik Reinfeldt tried to bond with the Greens as a mean of securing Parliament majority right after the election.