Is money earned from teaching the Quran permissible if the female teacher or students are absent and this is compensated for later without informing the parents?

You are entitled to the wage for the days when some students are absent from the study session, because you were available, dedicated your time, and ready to teach, and it was they who did not attend.

As for the days you are absent, you are not entitled to their wage. However, if you agree with the parents to compensate for these days, then there is no harm, and your full wage will then be permissible for you.

This is based on Al-Nawawi's statement in "Rawdat al-Talibin": "If the hired person surrenders himself and the period of possible work passes, the hirer is obligated to pay the wage." And Al-Hajawi's statement in "Al-Iqna'": "He is entitled to the wage by surrendering himself, whether he worked or not."