do you guys think my sister is suddenly allergic to my dog becuase shes smoking?

It could be, but I don't think so. People develop allergies throughout life. My sister was fine with walnuts until about a year ago, now her throat closes up. People develop new allergies as they age.

People can have their allergies change roughly every 7 years. So if she is around 14 or 21, it is possible that she has suddenly become allergic to dogs (unrelated to smoking).

However, I think it is much more likely the symptoms she is experiencing are directly caused by smoking. Breathing in smoke, as well as the thousands of chemical additives in cigs, can certainly cause strange things to happen to her.

Your dog is smoking? Put the dog out. LOL seriously though, the answer is no. Smoking leads to flu or allergy like symptoms.