。
She has the ability to do two things at once.
Literal
She [topic-は] one-time [at-に] two-things [object-を] do ability [object-を] possesses.
A formal, slightly bookish framing for what casual Japanese would render as 二つのことを同時にできる. 一時に (いちじに 'at one time, simultaneously') and 二事 (にじ 'two things/matters,' here functioning as a noun) lean classical-Chinese in flavor — 二事 in particular almost never appears in casual speech. なす is the literary equivalent of する ('to do, accomplish'), preserved mostly in set phrases and elevated prose. 能力をもっている fills out the formal register; everyday Japanese would more often use ~ができる ('can do').