Joined an unwelcome but not unexpected club this week

I havent done much research, but from what I've read, the "fake sugars" trick the body into thinking that it is still sugar, and the internal organs act as if it is sugar.
Wife is borderline diabetic, she is on Metfomin. She drinks Diet Dr. Pepper like a drunken sailor. She claims it is not bad for her. Is she pulling my leg!????