Hello and welcome to the community @Hannahblu, that is unfortunate to hear that this has happened to you. Do you happen to have any screenshots of your progress or completion of the event?
As @Alansmart mentioned, screenshots are always helpful but in this case, we know we had technical issues and the Quest disappeared for some of our players. We have released a fix that should solve the issue and bring Olivia back to your game. Please make sure you install the latest version again.
We are unable to add some extra time for you to unlock Olivia, so if you haven't had time to unlock her before the event ends, please post your game ID here and we'll see what we can do!
I'm going to close this conversation for now. Please comment here for any more assistance/question!