I've also got younger ones, but back when I did high school, pre-calc was the easiest of the high school maths. The first half is generally review, and the second half trig. If she was struggling in Alg II and didn't get the concepts/automaticity/etc., you may just see that repeating itself this year.
By this stage, she should start checking every problem on a test. For a tough exam, it's good advice to skim through the questions and start with the easiest ones. Move on to the harder questions. Then, always, always save time to go back and check answers. Having a good strategy for exams will help her confidence.
Also, how does the homework go? If she's struggling, do you see that in HW problems? By college, generally you decide how much homework to do, so it's good study practice to learn that when you're struggling doing extra homework will help. Math is a lot of practice, and with more practice, her performance will undoubtedly improve.
