this may be too late, but try VIGOROUSLY rubbing it with a towel. softly won't help as much. you can also support its back and kinda fling it forward and downward in your hands (this is really hard to describe, sorry) - the goal is to force any liquid out of the air passages without hurting the kitten.
but sometimes, they're just stillborn, and no amount of intervention will help. with such a young mother, who is small and inexperienced and was carrying a lot of kittens, there may have just been one baby that wasn't strong enough, and that's not your fault.