when I click l' insegnante it comes up with 'pay attention to the gender' and corrects to la insegnante, why is l'insegnante not accepted?
You are right, l'insegnante should be accepted, for either gender. Here Duolingo is mistaken.
La insegnante (without the elision) is ungrammatical, as clearly stated also in the grammar section of Zanichelli's website (http://aulalingue.scuola.zanichelli.it/benvenuti/2014/03/06/ripassiamo-luso-dellapostrofo/ see post dated 23 November 2015, 19:03)
It is the third time in a year that this issue has been brought up, but apparently Duolingo doesn't 'pay attention'. :-)
No need to buy a streak freeze yet... but your Italian is already excellent.