Looking at it positively, if Ryanair do split you all up, @PookieDo, that means there is every chance that one of the three you will end up sitting next to a woman, so that your dd could swap to that seat - maybe if she thinks about that, it will help quell her anxiety somewhat.
I suffer from anxiety, and I know that, even when you know that your worries are groundless, it is very hard to overcome those intrusive thoughts.
A couple of things that really helped me that I learned during Cognitive Behavioral Therapy were meditative, mindful breathing, and visualisation, and these are both things your dd could practise on her own, and might help her.
With the breathing, you close your eyes, and breath in and out deeply. Focus on each breath - the sensation of the air moving in and out, the movement of the muscles, the rise and fall of your stomach - and just keep on doing that. Thoughts will come into your head - maybe anxieties, maybe just things that are on your mind - don’t worry about them, just acknowledge them, mentally put them to one side, and refocus on the sensations of the breathing.
Visualisation - again, close your eyes, and take some relaxing, deep breaths, like the meditative breathing above. Then think about your anxiety - picture it in your mind (my therapist suggested seeing it as a dark cloud, but I tended to sense it as a feeling of weight in my head - there is no right or wrong here). Once you have that picture, look at what you can do to change it and make it better - if it is a dark cloud, picture it lightening at the edges, with the light gradually eating away the dark until the dark cloud is all light. For me, I visualise the sensation of the weight getting lighter in my head - pressure lifting - and that helps me feel better - less anxious.