。
She had a fever and felt hot all over.
Literal
She [topic-は] fever [from-で] body [subject-が] grew-hot.
で here marks cause: 'because of fever.' ほてる ('grow hot, flush') is an intransitive verb describing the body warming up — distinct from 熱くなる ('become hot') in connotation, leaning toward feverish flushing or embarrassment. 体がほてる is a stock collocation.