。
She's looking forward to seeing him again.
Literal
She [topic-は] him [to-に] meet-again [nominalizer-の] [object-を] enjoyment [as-に] is-waiting.
楽しみに待つ ('await with pleasure, look forward to') uses 楽しみ ('pleasure, anticipation') as the manner adverbial — に marks the manner. The whole construction frames the waiting as joyful anticipation. 再会する ('meet again, reunite') is a Sino-Japanese verb; the embedded clause 彼に再会する is nominalized by の to become the object of 待つ ('wait').