I can't imagine why she wouldn't renew unless there was something else going on. Maybe her family pressured her into not renewing because it might out the rest of them for being here illegally. A 21 year old working to support family has a lot of pressure. Obviously, she's kind of screwed now.
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Late 40's Dreamer (Holy Fucking shit I'm almost 50 and still dealing with this), aged out of original DACA and didn't have a chance to apply for extended DACA after Republicans killed it on the vine.