LA: Damage reduction isn't normally worth a +1 (according to Savage Species), but combined with alternate form, I'd think +1 more than the centaur is reasonable.
There are a few significant differences between this creature and a centaur, especially the extra hit dice, and the fact this is a fey creature instead of a monstrous humanoid, both of which more or less reduce the LA. A LA of +2 (ECL 9) might be ok.