I need advice! (Mother in law problems)

Mother in law back in march because she was being abused by her ex husband in another state and it wasn't safe for her there anymore. Living with her isn't that bad. She cleans, she cooks, she buys her own groceries, but her ethics and morals drive us nuts. Our baby is due in 3 months!! I'm almost there! She's a smoker and I can't stand it. No she doesn't smoke in the house, but I can smell it on her when she comes back in the house and it's so strong I gag. When the baby comes I don't even want her holding him if she has had even one cigarette. I've expressed this to her but she's impulsive, immature and stubborn. We have a feeling she's going to flip out on us when the time comes and we have to keep telling her no. I can't take this stress and we aren't getting our new place (with out her) till August. How can I deal with her craziness AND a newborn...please tell me if you have any thoughts or advice to give me some sense of calm.