User blog comment:IamJakuhoRaikoben/Chapter 388: Erza vs. Minerva, Review./@comment-5598380-20140613133747/@comment-24800928-20140617202848

I mean she has been using this power since birth. What if she already was able to use her power to the best of her abilities, but it took an extra something to push her power to the point of her mother's. The dragon slayers didn't train to obtain dragon force, they found (by eating their element) a way to amplify their power to trigger it.