How to approach this...?

My mom has quit smoking for 3 years but recently slipped up and has been continuing to smoke. She knows that I know she had slipped up but she won't tell her doctor that she had started smoking again. I don't like that she won't because she's lying to keep her insurance cost down and I think it's wrong to do that. She says that she's on medicine and won't continue to smoke but I know she still is and has cigerettes in her purse. How do I tell her to stop lying without being rude? I just get so heated to know that her morals are like that.... Help me!!!!