。
I don't think she can speak French.
Literal
She [topic-は] French [object-を] speak [thing-こと] [subject-が] cannot-do [quotative-と] (I) think.
This is a compound assertion: the embedded clause '彼女はフランス語を話すことができない' is the speaker's belief, and と思う marks it as the speaker's opinion. The negative potential ことができない ('cannot do') is the formal counterpart to 話せない. In English, '(I) don't think she can speak French' is more natural — Japanese here keeps 'I think' positive ('I think she cannot') rather than negating the thinking. This structural difference is a classic stumble for translators in either direction.