As someone with experience doing this exact kind of job…
If she knew it was against store policy for employee consumption beyond what a supervisor gave her to sample (which was generally how we became familiar with the product) then, yes, it’s a firing offense. Mine was a union shop, and this is exactly the kind of thing they wouldn’t lift a finger to help you on, justifiably.
However, if there was even an informal company culture of this, and she had no warning, then the company is acting horribly. I prevented someone from getting fired once, when she grabbed me at random to play witness to her disciplinary hearing, when instead of just silently observing that they were being “fair”, I pointed out that what they were trying to fire her over was taught to me as an unofficial practice when I was hired (before her), and that management knew about it.
As for wastage, it is huge, and sickening. But that’s not an excuse, here. Maybe we need to change those practices, but that will come at an institutional level. And yes, I know the heartbreak of being in food stamp level poverty and giving away free food to someone whose jeans cost more than you’d make in three months. Because our store policy was to give away the leftover prepared food to anyone other than staff. Want a $4 chicken pot pie, made fresh today? Here you go, just let me mark that NC for you. (We compromised by giving them to people who worked at the Starbucks next door, as often as we could get away with it. They reciprocated as often as they could).
It sucks, but I have to say, I am not surprised. In an industry where they will fire you for being thirty seconds late back from a break, this is well across the lines.
Is it right? That’s a different debate. But it’s common.