I hope Veronica doesn't hope to interact with Hajime ever again. She was the one who purposefully took Lily in, despite having witnessed her black-eyed power, at least to some extent (controlling a bunch of monsters). Yet now Veronica's using the treaty against him, to make him pay for what was essentially her own mistake.
Considering it from a purely legal point of view, that ancient type guild treaty must basically be designed to prevent anyone from exploiting the ancient types. Hajime's case here is a mere side effect Veronica chose to put to use, to make someone else pay for the repairs, even though logically it was her own fault. It's the kind of legal loophole in the same spirit as those that allow billionaires to avoid paying any taxes, for example.