She won’t stop smoking around me

So I’m currently 15w4d pregnant and my MIL will not stop smoking around me. I’ve asked her countless times so has my husband and her response is always “I smoked while I was pregnant and they was fine”. It concerns me that the baby will have something wrong with its lungs cuz of this. I told her if she doesn’t respect my wishes that I will not come over and when the baby is born she will have to come to our house. She says im overreacting and it’s not a big deal. It just really upsets me 😔