It turns out that in 1867 when Dym was published,
Marina was 23 years old and presumably no longer governed by a governess. So she
is probably prevaricating both in reference to borax and Smoke.
Since the hypothetical contravention might or might not have
occurred when she was "Van's age" (i.e. fourteen) that would have been in 1858.
Marina's governess probably attempted to ban Madame Bo-vary, whose
author was brought to trial in 1857 and/or Fleurs du Mal, which
brought its Bo-author legal grief in the same year. Dym is a
prevaricator's smoke screen.