How old is she and what level is she? How is she doing at school both academically and socially? At gym and school (and anywhere else) is she under a normal amount of pressure or too much? What does it mean "she only had a few days to clean up her bar routine" - or what would happen?
Here is my thinking. Plain old situational anxiety (as opposed to an anxiety disorder) is a normal reaction to life, which normally requires that we do things that are difficult and thus are normally anxiety provoking. It is how we react to anxiety that is the problem. An anxiety disorder (or any other diagnosable disorder) means the anxiety (or whatever) and the person's coping mechanisms are interfering with life. For example, a child with anxiety about some aspect of going to school might refuse to go to school because they have learned that avoiding school lessens their anxiety.
If she is ONLY having situational insomnia- not being able to get to sleep occasionally when anticipating something that feels (and realistically is) more than typically stressful, but she is otherwise functioning normally and doing the normal things that are required of her without much difficulty, I am not sure you have to do anything except maybe listen to her fears and reassure her. Worrying about not getting enough sleep often only adds to the anxiety.
For just general difficulty getting to sleep, I agree with trying the little (or preferably no) screen time for a couple hours before bed. When he could not get to sleep for a while, my son benefitted from visualizing a peaceful place and deep breathing. It helps to encourage them to experience the place with all senses, not just "seeing" but also hearing, smelling, touch/feeling, etc. When that did not work, he would do the thing were you start at your heals and slowly "breath into" or relax each part of the body, in turn. If they are old enough they can do this themselves, but youngers will probably need to be guided.
Also sleep patterns change as a child ages, sometimes dramatically. If a kid is being asked to go to bed "too early" for where they are developmentally, that can make it very hard for them to get to sleep. Again, this would be indicated by frequent, not occasional insomnia.
Mindfulness and the ability to focus on the present moment is really helpful for anxiety. We use the Headspace app.
