I understand that she feels bad about electing French and not German in her schooling, as German would have proven more useful, if only she could have evaluated the future a little better.
Mentionning explicitely the choice that failed to be made is a common way to express this in French:
- Quelle idiote d’avoir choisi d’étudier le français !
Word for word: What a fool to have elected to study French!
What it means in more coloquial English: Why did I choose to study French?
- Dire que j’ai étudié le français, quelle nulle !
What it means in more coloquial English: ...and I studied French! Such a silly girl!
1° Unlike in English, names of languages in French start with a lower case letter (anglais, français, islandais, japonais, russe, etc.).
2° A non-breaking space is used in French in front of punctuations that use two signs (as the colon, semi-colon, or in this case the exclamation mark). I don’t think anyone will pay too close attention to that detail when the main text is entirely in English, but you have a choice here to make it that bit more exotic by enforcing the French rule for the French sentence.
3° Other choices are possible, of course, and the votes and comments should (hopefully) ultimately allow the best choices to move ahead of the less satisfying ones. These last few comments will however apply to any past and future proposition.