"Livia feels poorly."
Translation:Livia se male habet.
No, it's literally "Livia has/holds herself badly."
The Spanish is literally "Livia feels herself bad."
The reflexive is needed in both because otherwise what is she holding? What is she feeling?
Since "poorly" is an adverb, it modifies the verb. Hence, the English here is a statement about defective sensation.
"Livia feels bad" should work.