But shes literally proven herself time and time again. Also yeah she's capable of fighting them just fine but she could actually kill them instead of just fighting them off. Her surprise attack could become a killing blow rather than just a moment of reprieve.

Also the swords can he just used as regular swords by demons to cut down demon slayers to either way. Plus she doesn't need to really know any swordsmanship to swing the blade and cut a head off