Hmm? She says "more than two thousand years ago" but the grandmother should have been born only 1993 years ago.
Are the MC and previously her mom the only witches in existence? If the grandmother was at one point the only survivor and witches only leave one offspring each. In that case was the anti-witch force de-facto an "anti-Mom force" for the past millenium? But all other dialogue points to witches being more common than mostly just one person. Why are they called witch-"hunters" if they haven't succeeded in taking one down in two millenia? Because it's a trope?
I hope this part of the worldbuilding clears itself up. Everything else about this is not that bad.