。
She has been studying French for several years.
Literal
She [topic-は] several-years French [object-を] is-studying.
数年間 means 'for several years' — 数 (several) + 年 (year) + 間 (span). フランス語 (French language) uses the 語 suffix common for language names. ~している marks an ongoing action that started in the past and continues — the Japanese present progressive handles what English expresses with the present perfect continuous.