。
She was there the whole morning.
Literal
She [topic-は] morning-during continuously there was.
午前中 + ずっと doubles down on the 'all morning' span — 中 ('throughout') already covers the period, and ずっと adds the unbroken continuity. The pair is mildly redundant but completely natural — Japanese often layers temporal markers for emphasis. 'For the entire morning, continuously there.' Compare a single 午前中そこにいた ('was there during the morning'), which doesn't carry the same insistence on continuity.