mother in law smokes in the house

my son and I are currently staying withb my mother in law at her house while my husband is deployed. I'm 29 weeks pregnant and my son is a year old. she smokes in her room, but the smell of the cigarette travels thru the whole house. her roommate also smokes in his room and it sometimes goes in our room since it's next door. whenever I'm out with my son, I come home to them smoking in the living room. the smell gives me headaches. idk how to approach her and tell her how bad second hand smoke is to not only me but my son! It is her house so I don't want to seem like I'm complaining