。
She slowly closed the diary.
Literal
[topic-は] slowly diary-book [object-を] closed.
ゆっくりと is a state mimetic for slow, leisurely, unhurried motion — used adverbially with the optional connecting と. Distinct from のろのろ (which carries a slightly negative sluggish flavor) and ゆるやか (more about gentle gradients). 日記帳 ('diary book') is a compound: 日記 ('diary') + 帳 ('notebook, register'); the suffix 帳 productively forms names of bound notebooks (手帳 'planner,' 通帳 'bankbook'). 閉じる ('to close') applies to anything that opens and shuts — books, eyes, doors, deals.