。
She's really good with a saw.
Literal
She [topic-は] saw [object-を] use [nominalizer-の] [subject-が] very skilled-at.
[verb]+のがうまい is the standard pattern for 'be good at doing X' — the verb is nominalised with の, marked as the experiential subject with が, and predicated by うまい ('skilled, good at'). うまい has the same structural role as 上手 here, but is an i-adjective rather than a na-adjective and tends to feel slightly more colloquial or direct (it also means 'tasty' in food contexts). のこぎり ('saw') is written in hiragana here but has the kanji 鋸; tools and household items often appear in hiragana when the kanji is uncommon or rarely used.