。
She was supposed to come here by noon.
Literal
She [topic-は] noon [by-までに] here [to-に] come [arrangement-ことになっていた].
~ことになっている means 'it has been decided/arranged that' — expressing an established plan or expectation. The past form ~ことになっていた means the arrangement existed in the past (she was supposed to come but perhaps didn't). までに marks the deadline: 'by noon,' distinct from まで ('until noon').