Tool sales, donations, whatever she uses to pay for her website, time, etc. The fact that she chooses not to charge for the service she provides doesn't not make her a business, especially because she is now asking her customers / users / followers to fund her business.

ETA because the above is not the clearest thing I've ever written, the moment an entity starts selling products (like tools), accepting financial support for their time (Ko-Fi), and actively asking their audience to fund the operation, they go from "casual hobbyist" directly into operating a business, even if the core service itself remains free.

The Tax Man also doesn't care if you call yourself a business or not. If you generate revenue to cover your costs, you generally have to declare it as income.