I think seeing a therapist is a great idea. That person will help your DD explore the triggers and come up with some practical solutions. I agree, find someone she likes and is comfortable with, and someone who works with people in her age group.
Someone here on the Dis posted this reference book once, and I've actually given it to people I know who have anxiety, and they found it helpful. It explains that having a panic attack escalates because the adrenaline causes you to feel like you're having physical symptoms, but they are based on no real threat (such as would be needed for fight or flight based on a real threat). There are a lot of worksheets and chapters on self-help.
https://www.amazon.com/Anxiety-Phobia-Workbook-Edmund-Bourne/dp/1626252157/ref=dp_ob_image_bk
And I agree with the recommendations for learning to regularly practice complementary habits like yoga, mindfulness, relaxation techniques, visualization, even prayer (the #1 complementary therapy), etc. The reason they work - and this comes directly from the mouth of the Father of Mind/Body Medicine, Dr. Herbert Benson, whose Mind/Body Medicine course I attended at Harvard Medical School - is because it is literally impossible to worry when you have to concentrate on something else, such as holding a yoga pose, kneeling and praying, or standing on one foot like some monks do. The more you practice relaxation techniques, the better you get at pushing intrusive thoughts away, but it must be practiced. I had to learn this myself when I was in cancer treatment, so I could actually make it through the sessions. I also used some of these with my son in his sport - if a mistake was made, you could see the whole team's heads went down and errors started to happen. I taught him (and later the whole team) a visualization to "sweep it away", literally visualizing a broom sweeping thoughts away, then repeatative words coming in to replace those thoughts that said, "One play at a time". This worked really well for him/them as they learned to automatically reference it. We can all learn to do the same with some practice.
There is another book, called The Wellness Book, that I think might also be helpful. I would buy both for your DD, and I think you will enjoy it, too. Dr. Benson is one of the authors.
https://www.amazon.com/Wellness-Book-Comprehensive-Maintaining-Stress-Related/dp/0671797506
Anxiety for women can get worse at certain phases of their cycles due to hormones, so something to be aware of and perhaps track. They address this in The Wellness Book.
Good luck. It's great that you're helping your daughter.