Double Leaf is not a fool, nor does she like to play dumb when it's unnecessary. Therefore, the fact that she can disregard Diana's advice to engage with things that may induce 'danger' proves that she has enough confidence to mitigate those risks.
For instance, going to the forbidden book section to check out things that might not actually be 'taboo', but do contain some non-mainstream 'knowledge'. After a fairly thorough investigation, Double Leaf concluded that with a bit of caution she would never find herself in a desperate situation.
Of course, this conclusion, not yet tested in practice, might not be correct. However, as long as the general direction is not problematic, she is never averse to taking a slight risk.
This level of analysis, although they 'only knew each other for a few days', Frank, who had at least gotten a little familiar with Double Leaf, was still able to achieve.
And so—
"Alright, I understand."
