Not a native speaker, so take with a grain of salt unless someone verifies:
But, I think it's because of passive action in the Russian sentence. It's not about her hurting her hands or injuring her hands by her own action - her arms hurt on their own, through no fault of hers.
Ok. The conjugation/declension app I use has it conjugated differently though, like болею, болеет, болеешь, etc. 2 different verbs with same infinitive but different conjugations? Or are the 2 infinitives stressed differently, i.e. бОлеть vs. болЕть? Strange that my app doesn't appear to even have the one that's conjugated оно болит...
There are two verbs but they're both pronounced болЕть. The one used here means to hurt, the other has various meanings including to be sick, to be anxious or to cheer for. That one has conjugations in болею etc. Check out Wiktionary: