I can hazard a guess or two, based on experience.
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She got caught, and management wanted to make an example of her.
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Someone reported her to management, and they didn’t want to be seen as “soft” or “setting a precedent” so fired her.
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She was a “troublemaker” in other areas – talking about unionising (or talking up the union, if it is a union shop), refusing unsafe work, or simply not being droneish enough. Or maybe she was a genuine PITA.
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A new manager came in, and choose from 1, 2and/or 3 above.
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With nine years seniority, she was getting expensive, compared to a new hire. Combine with any or all of the above.
Retail grocery lives on high turnover. They hate long-term employees, no matter how much they say otherwise. Doesn’t really matter the reasons, she gave them an opening, and they took it. If it is a union shop, theft (even a couple of pennies worth) is a gift to management, because the union will not contest it. Multiple write-ups are not required. It’s an instant escort to the door. It’s one of the first, fast lessons you learn.