Lets unwind some threads of the problem here.
You, quite rightly, don't believe your daughter should become a gender stereotype.
In MILs culture women run around after men, you don't want that to be absorbed even unconsciously.
But in this particular situation she is doing something she loves with people she loves and who love her.
You can't cook the dishes but she will have them memorised by the time she is 10, so if she chooses to have children in the future they can be passed down a generation - that's quite a cultural heritage.
There is also lots of potential for pointing out that a 6 year old girl can do things better than a 40 year old man and how ashamed he should be (all done jokily).
I think this is not about tomorrow it is about her future and she needs to know it is her choice to cook, that she doesn't have to run around after anyone.
Think about when she is 14, and doesn't want to help, you can back her up to the hilt and say that as your dd has a dual heritage she can express either at any time, and in your culture you don't cook Spanish food and run around after the men.