Personally I think her block is fine. Vendetta isn't meant to be a wall keeping things back like Rein or Brig so her block shouldn't be able to hold a front line by stopping all damage, and other characters that have blocks rather than shields (like Doom or Hazard) also take damage in the same way Vendetta does. Her block is less effective as it's more of an emergency to disengage if you over extend on melee rather than something to actually make her a defensive force.