Okay, this article explains the vote was passed with overwhelming yes votes, 420-9, so she could have voted no and it technically would've had no impact on the votes passage. Many of her liberal fans were upset that she didn't vote with the rest of "The Squad". This article suggested that she likely has higher political ambitions, and I tend to agree. She didn't want to register a vote that she could get nailed for down the political "road" (a la Sen. Hillary Clinton and Iraq), so she basically abstained. Unlike HRC, who has always been a moderate and fluid on a number of positions, AOC has always been vocal about her steadfast dedication to take certain political positions, so, in a way, she set herself up for this blowback, by setting her bar so un-negotiably high that anything less would be considered to be backing away from her avowed principles.
https://www.seattletimes.com/nation-world/alexandria-ocasio-cortez-apologizes-after-tearful-present-vote-on-israel-iron-dome-funding-bill/
Also, this Iron Dome spending, worth a billion dollars, can pass but not another round of stimulus checks??!