First thing first, even though Marlo Thomas is 76 years old, her face looks so smooth and wrinkle free. According to expert plastic surgeons, she had botox injection and face lift operations. Based on expert plastic surgeons' ideas, having such chubby cheeks, not having any wrinkles on her forehead and her face at the age of 76 are simply results of face lift and botox.
Moreover, expert plastic surgeons think the change in the shape of Marlo Thomas's lip can not be without lip filling injections. Lip filling injections make a lip look wider and thicker than before. If you check the photos before&after, you may notice that Marlo Thomas has wider and little bit thicker lip now.
Finally, despite the fact that, Marlo Thomas does not admit having plastic surgeries, one can easily see the change on her face over years thanks to plastic surgery.