The quote is implying that Marie Antoinette was uninvolved in politics, I think, and therefore was not guilty of what she was charged with (treason). She certainly didn't deserve to be executed IMO, but she was certainly involved in politics.

What's important to understand is that the French had a thing called Salic Law, which didn't allow women to reign as monarchs (unlike, for example, England which had both Mary and Elizabeth I). This meant that the reigning monarch was regularly married off to a foreign-born princess, which created excellent diplomatic ties with often previously antagonistic rival kingdoms. M-A was Austrian, from the hugely powerful Habsburg dynasty, so the marriage was originally seen as an excellent way of uniting those two superpowers. M-A's links with the Austrian emperor, her brother, would allow the two houses to negotiate effectively and create political alliances.

However, these kinds of marriages ALWAYS led to the queen being accused of being more loyal to her homeland, and secretly dealing with foreign rulers. So M-A's letters to her Austrian family (exactly what she was supposed to do) were used as evidence against her that she was secretly plotting France's overthrow. Coupled with the generally wildly misogynistic and pornographic libels that were being pumped out at the time, which accused her of everything that previous French queens had also been accused of (incest, lesbianism, murder, etc), M-A never really stood a chance once revolutionaries had decided that the royals were to blame for everything. It meant that she got more blame for things than the actual ruling king did. The difference in tone between the execution ballads written about M-A vs those about Louis XVI is remarkable: he's a 'foolish child' who let things get out of control, whereas she's a 'devil-witch' who planned to murder the French.

So the answer is that she was involved in politics, so was not ignorant, but she had no genuine power to effect change as a non-ruling monarch, so didn't deserve her execution unless you think (as some revolutionaries did) that all royals should be executed.