。
She hardly ate anything.
Literal
She [topic-は] hardly anything [object-を] did-not-eat.
ほとんど + negative is one of Japanese's standard 'hardly / scarcely' patterns — paired with 何も it intensifies into 'hardly anything at all.' Standalone ほとんど in a positive predicate means 'mostly, almost'; what flips it to 'hardly' is the negative predicate. This polarity flip is a recurring feature of Japanese frequency adverbs (あまり~ない 'not much,' なかなか~ない 'hardly'). The sentence reads as a clinical or narrative observation — possibly worrying, depending on context.