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First off, your story sounds pretty cool.

Second off, to answer the actual question: not making her the only person who doesn’t want to be Thunderstruck might help. Let there be groups of people who want to be and groups who don’t and groups who just don’t care. Another thing — this will depend on how the Thunderstruck person is chosen — would be to have her take action to avoid becoming Thunderstruck. If there’s no human intervention, maybe you could have her make a point of planning to stay inside and avoid any chance of being struck. Or if it’s more of a “the town elders pick the most likely people to stay outside,” have her try to avoid their notice, maybe try to skip whatever meeting or event the potential Thunderstruck people are announced/chosen at, that sort of thing.

Also, keep in mind that readers will probably expect that your protagonist will be Thunderstruck no matter what you do, because that’s just how stories work.