You cannot be logged into the Battle.net account at the same time, but you can log into two different WoW licenses on the same Battle.net.
While she can play on the account I would recommend that you create one for her. It will allow you to set up parental controls on the account that will not otherwise impact your ability to play. You can control if she has access to social channels, Real ID, etc… and of course your own BattleTag/RealID chat won’t go to her if she is on a different Battle.net account.
It also allows for her to have her own collection of pets and mounts that would not be impacted once she turns 18 and has to split off to her own Battle.net account at that point.