She hugged the baby in her arms.

Literal

She [topic-は] baby [object-を] arms [in-に] held-tight.

抱きしめる (だきしめる) is 'to hold tightly' or 'to hug' — the compound of 抱く (hold) and しめる (tighten). Where 抱く alone is neutral holding, 抱きしめる adds physical intensity — a tight, protective embrace. The past tense ~た makes this a completed action rather than an ongoing scene.