Anxiety is about thoughts. Your daughter is having a lot of fearful thoughts. These thoughts are causing deep fears and they are starting to show up in her body.
Listen to her. Support her by saying: "Tell me about..." Then listen. Do not provide platitudes or solutions. Just listen. Let her spill out her fearful thoughts. This is a good time to just hold her and let her pour out her fear by crying or shaking or whatever she needs to do to fully feel the feeling that is being created by the fearful thoughts. Just hold her and let her feel your support and safety while she feels the feelings. Don't shut down the feelings just because they seem powerful and overwhelming. It is extremely important to allow her to let the feeling pass completely through.
After she has felt the feelings and feels calmer, then ask her: "What will happen next?" Let her use her imagination. If she says: "I don't know," just ask her to imagine what would happen next. Then ask her again: "And then what would happen?" Ask this until she gets to the place where everything is okay.
With anxiety, we get stuck in the worst case scenario. We play it out in our minds over and over again. We can stop the cycle by moving forward in time. Every crisis, disaster, or tragedy comes to an end and time moves forward. With anxiety we get stuck. It is helpful to create a space to mentally move forward in time to see the solutions.
Another tool is a The Work by Byron Katie. She has an incredibly powerful process to question our fearful thoughts. She has a children's book called, "Tiger, Tiger Is It True?: Four Questions to Make You Smile Again." It is a lovely book that you can read to your daughter to support her in learning how to see her thoughts and start to be more curious about them rather than buying in to the thoughts and becoming fearful.
Curiosity is the antidote to fear. Support her in being curious about what she is believing about the world. Another exercise you can do is, when she has a problem, ask her to come up with two solutions. Let her be as magical and mystical as she wants. Then you come up with two solutions. Again, be magical and mystical at first. Then try it again. Eventually slip in some more realistic ideas although ideally she will be the one to do this first. Make this a curious, playful, fun and imaginative exercise. You want to shift her energy from fear to curiosity.
How much anxiety do you have? Are you a worrier? Do you watch a lot of news with her within hearing distance? Does she hear you talking on the phone or having conversations with other people where you are complaining or worrying? Sometimes we are not conscious to how much of our own fear we are exposing our little ones to. It might be helpful to take a little time to be curious about your own fearful and anxious thoughts and how those may be getting transmitted to your daughter. Also, observe the other significant people in her life and see where else she may be picking up these types of anxious thought patterns.