Without taking gender into account, the word relentlessness sounds more like a negative trait than a positive one. They're someone who's unwilling to deviate from their plan of action, because their plan is to just head straight for the goal.
I'd go with dauntlessness, someone who's dauntless won't let an obstacle stop them, but will go around it instead of through it.
I'd go with dauntlessness, someone who's dauntless won't let an obstacle stop them, but will go around it instead of through it.