Oh gosh. Where to start!
I'm 44 and have been phobic for a good 40 years. It affected me very badly at school.
This time of year is terrible for true phobics, I really sympathise - with all of you, because its not easy being around someone who is phobic either.
There are 2 things that can be done right now - the first is to get some CBT for her. It will help her understand catastrophic thinking, help her to rationalise panic attacks and not be frightened of the sensations they bring, and start helping her get back in control of some of those awful fears.
The second - and I'm not sure how applicable this is, given her age - is to ask her GP to consider some mild medication. It really takes the edge off the anxiety, staves off the panic and helps to face things a little more logically. Now that may of course not be an option at her tender age, but it's worth mentioning as I know my over reactions start to recur if I go more than a few days without my tablets. I've taken them solidly for 18 years, and sometimes in winter my GP increases the dose slightly. But I have a fairly high flying career, so don't be afraid of it affecting her badly for all of her life! I had some terrible times, true, but I came back fighting - it can be overcome, with practice and some medical help.
If she is currently nervous about noro...I have a handy statistic for her. There was a noro epidemic in 2007, when the media helpfully predicted that 3 million people would catch it and all the emetophobes went into meltdown. My phobic doctor pal worked out that this was about 0.4% of the population. Less than 1 in 10. I personally found that much easier to handle than 3 million people, and no one I knew got it either.
Try not to "feed" her fear by making a big deal of it - on the other hand, when you can see it is eating her up (she may be pale, withdrawn, reluctant to eat or talk) you can reassure her by ensuring everyone at home is religious about hand-washing before eating. Let her see you casually bleach door handles, light switches, loo handle, taps, stair handrail. Change towels regularly. Get her anti viral foams and wet wipes that kill noro (must contain benzalkonium chloride - Wet Wipes do, as does Boots anti viral foam, but baby wipes and anti bac gel do not) - she may feel a bit stronger knowing she has those for her hands when she feels anxious. This is not feeding it - it is giving her tools to cope and not dismissing her, believe me!
If I think of anything else I'll be back, but ask me anything you like. See if she will open up about specific things which make her most anxious.