Sport and Performance mental coaches can be certified and do a good job, but a psychologist will have more training on the mental health side of things. Anxiety, in many ways (but not necessarily all) is an intolerance of uncertainty. There are sport psych tools for mitigating this.

One example of what comes to mind for me is developing a good pre-performance routine, and when I say "pre-performance" I'm not talking about hours before, I am talking about at least a week before, and everything leading up to hours before. A good sport psychologist can help her develop a plan that includes mental imagery, self-talk, sleep schedules, and diet that is predictable, and consistent to help diminish the uncertainty before a performance. The pre-performance routine goes from broad things a week out (as described earlier) to very specific imagery and self-instruction just before the performance. Most olympic athletes are going through their routine on screen just before they begin. You'll see them mouthing instructions looking in specific directions and repeating intentional movements.

Anyway, that's just one idea that assumes the anxiety is a performance issue and not something more (based on your post it doesn't look like the symptoms show up outside performances).