WHAT

Yep, she is broken from all the beating and she tought that the only way Ye Zi and her wouldn't be beaten anymore is something like that.

Shes performing a Mass suicide wherein the smoke of the fire or any chemicals that is dangerous for your health when inhaled will cause them to die due to lack of oxygen (Since she covered up the opening of the house with clothes and etc)

i think she didnt want that her son and she to live a life full of pain , so after they die at least they would die in peace and not in pain