Odd question ??

Okay so every time we have a family gathering on my husbands side that is, his mom brings plastic containers with her, why do ask?  Well to take the food that I spent all day cooking home with her!!!  Is this odd?  Because she does it every time,  who does that?  I'm just wondering is this what mother in laws do?  did I miss the memo somewhere or is this not in common at all??