Hello and Happy Sunday. It sounds as though your daughter has the abilities to do well but she is not applying herself as much as she should. You already have a tutor for her which is great. Additionally, she should be meeting with her teachers for further assistance and a review of testing errors. It also helps when a student has a study buddy or studies with a small group of friends.
Furhtermore, you may also want to have an open and honest talk with your daughter about how she feels while taking the tests and about school overall. Does she feel like she studied enough? Was she overprepared or underprepared? Does she want to further her academic studies by going to college?
Also, make sure that everything is alright with your daughter socially. Sometimes, social difficulties can cause individuals to have problems focusing. What are the relationships like with her friends or boyfriend..if she has one? Have there been any major changes?
If she continues starts to do really well then she should be rewarded because she has put forth the effort to improve. If she continues to do poorly and you have exhausted all possible causes on you own, then you may want to speak with her counselor at school first and then possibly a school psychologist before you start taking things away from her. There may be a deeper rooted problem.
If you need more advice, just ask. Have a good day!!!