。。
She can speak French — fluently, at that.
Literal
She [topic-は] French [subject-が] can-speak. Moreover fluently.
しかも ('moreover, on top of that, what's more') is a discourse connector that adds a striking second point to the first. 流ちょう (流暢) here is written with a kana ょう instead of the kanji 暢 — a common stylistic choice for less-frequent kanji. The trailing fragment しかも流ちょうに is a sentence-final ellipsis: it ends adverbially with に, leaving the verb 話せる implicit from the previous clause. This kind of trailing addition is characteristic of natural spoken Japanese.