Every time my mum came over or we went there, she would give us groceries of some sort. When DS visits or we go there, I do the same! I buy in bulk so it may be loo rolls, washing up liquid, food that I know they like, or M&S vouchers so they can treat themselves. Probably, like my mum, your mum is just trying to ensure that you don’t have to cut back on something in order to host them. Accept with grace.
However, my brother offered me money when he and his family came for Sunday dinner once and I told him where to shove it. He did explain that it was because he felt guilty that my SiL would never invite us over.