Again, I think it is more of a plot device than anything else. If the bullet can go threw the INDESTRUCTIBLE bracelets, threw one side of her wrist and out the other, than go threw the other side of the INDESTRUCTIBLE bracelets and still have more than enough power to go threw Hephaestus's armor then finally piercing Wondys flesh (heart, not sure if it went there directly), then why did the bullet stop there? It seems like the bullet should just have kept going on and on and on.
And I never liked the centaur scene with the arrow. This is one of the reasons I felt she was depowered in her first issue out as she couldn't take the force of the arrow without getting knocked down. The same Wondy who has had countlessly more powerful attacks levied against her that she blocked and hasn't needed the ground to brace her fall.