i think you should directly talk to her about this and ask her if her maid can take up some of the cooking responsibilities.
on another angle, since you are visiting, maybe you can take the maid's help for breakfast and lunch, and prepare something yourself for your SIL for dinner. she will surely love this gesture after she comes back home from a tiring day. imagine yourself in her shoes, i am sure you too would feel happy and loved if she did this for you :) if you are absolutely not happy then you should go back before the relationship takes a bad turn.