I have given Charity about 15 items so far this year and I haven't received any items from her so far. I know she doesn't give you an item for every item you donate, but I have never gone so long without getting anything in return. Is anyone else experiencing this? Is this a bug? Should I report it as a bug? Or am I just very unlucky this year?

I have experienced this. It is not a bug. You should not report it. You are unlucky.

That said, I think her random number generator is kinda sticky. Me, I pause and go scratch a scratch card or something, or I try donating a different food (if I'm donating from a pile of cheapy foods I just snagged).

I could be wrong, I haven't done any real research on this, but I think last year, she was more likely to give out items for rarer food. This year, I've gotten like one or two items from her, but I've only given out things I've gotten from questing, which are generally on the cheaper/lower rarity side.

Could be a thing /shrug

I haven't done any research either, but I also gave her a lot a "junky" items, and I didn't experience what you did. My experience was more like where she seemed to "stick." I got a lot of items one after an other, or a bunch of none at all in a row.

its pretty random.