After her illness, she looked like a shadow of her former self.
Literal
After-illness [possessive-の] she [topic-は] as-if previous her [possessive-の] shadow [object-を] seeing [like-ようだった].
病後の ('post-illness') uses 後 as a suffix. まるで...ようだった is the simile pattern 'it was as if.' 以前の彼女の影を見る is the evocative metaphor 'to see the shadow of her former self.' A literary, descriptive sentence.