Fluoxetine suddenly stop working?

Hi all. Hoping someone might have experienced similar here. My daughter (8) was on 5ml(20mg) of Fluoxetine and 1ml of Abilify. Since May school has been great and summer a dream. Returned to school almost 3 weeks ago and still brilliant until Monday of this week she's back to bring extremely anxious and stressed in school again. School are fantastic, she's in an Autism class, very quiet, teacher lovely etc. Has anyone had experience of Fluoxetine just suddenly stop working? Because it feels like this happened overnight. Nothing happened in school. She's like a caged animal again like she was before starting the medication. Waiting to hear back from psychiatrist but was wondering if anyone else had experienced this? Thanks.