I thought about whether I needed to change that line for a while... after all, even in the original version, it's not realy clear that he's even saying "her" as the line gets sort of swallowed. I watched the speeder chase to see if Anakin ever got a good look at Zam, and I don't think he does. Since they don't have the conversation about "I think he's a she" in this version, Obi-Wan just makes the male-centric assumption.