So, just to be clear, the twintail sister with the unfortunate name tried to steal the potion, but Eris snuck in the "free sample" paper along with it and she didn't even notice.
Nobody can easily steal the lacquer technique anyway. It requires a source of the resin, after all. Just looking at the finished product will, at most, make people wonder how such a thing was achieved, but otherwise they would start from zero.