Ethical Dilemma

So I have an interesting situation that has recently developed at work....I have befriended one of our cafeteria workers who is a recent immigrant to the US. Befriended is perhaps an overstatement, I have just engaged in polite conversation each morning and afternoon and gone out of my way to go through her check-out line. She works ten hour days, 6/7 days a week! Her name is a challenge for an english speaker, so she always shows delight when I get it right. My interaction with her and a few other cafeteria workers has become my favorite part of each day.

So, in the past two days she has intentionally not charged me for my milk at breakfast (I always get a bowl of oatmeal and raisins, milk, and a cup of instant coffee (yek). The free milk is a small token of appreciation from someone who has very little to give. But here's the rub, its not her milk to give away! I really appreciate the gesture, and the impact on the food service company is clearly insignificant, but should I be accepting such an offer, especially if it becomes a regular occurrence?

Now I know the obvious answer here is to politely decline, leading to a moment of embarrassment on her part, and a rectified situation. For me, her warm greeting is worth many, many times more than the free milk, but I can't think of a way to graciously communicate that.

So, do I refuse such a small gift from an overworked, underpaid worker who likely comes from a culture where gifts are highly valued, with the alternative to basically aid and abet stealing milk from our cafeteria? Or should I find a way to reimburse the cafeteria coffers while continuing to accept her token gift of a free milk (thus reinforcing that this behavior is acceptable)? Or am I just being silly and should look a gift milk in the carton?

I for one do not think there is an easy answer here, but would like to get your input. What do you think I should do?