Here's MTM as Laura Petrie in "The Dick Van Dyke Show". Apparently she didn't light the cigarette in these pics. Kind of shocking at the time as she had a squeaky-clean image.
Mary was born on December 29th 1936 so she was roughly 24yo at the start of this show.
Found a pic of her smoking on the set of the movie "Change of Habit" with Elvis Presley in 1969 but the site wouldn't allow saving as it was "copyright", darnit!
Plus a few pics from other shows or movies & candids.