The most accurate description of Arianna's work is:
Arianna multiplied with the reciprocal of the dividend instead of the reciprocal of the divisor.
In her work, she correctly set up the fraction division but mistakenly multiplied the dividend (two-thirds) by the divisor (four-fifths) rather than multiplying the dividend by the reciprocal of the divisor. The correct operation should have been:
\[ \frac{2}{3} \div \frac{4}{5} = \frac{2}{3} \times \frac{5}{4} \]
This would lead to a different result.