Even taking the prequels into account, it still makes sense that Obi Wan has cashed all his chips on Luke as opposed to Leia, even if that wasn't the original intention.

Luke has already had training in the force with Obi Wan and then Yoda. Was Obi Wan going to suddenly appear to Leia and go "Hey time to learn the force" Also Leia had some military training in that she could handle a blaster, but she wasn't much of a pilot or showed jedi skills like Luke.

Mind you that explanation is completely retcon stuff since Empire was written without Leia being the Other at all. But with the prequels taken into account it still makes sense that Obi Wan doesn't consider Leia to be a credible choice to suddenly become a master Jedi.