My [ex] wife was willing enough when we got together. It was mainly the smoothness of better driving versus one particular aspect of the comprehensive whole (safety, insurance cost [accidents/tickets], vehicle longevity/reliability
and then fuel economy).
Establishing new habits takes time as most of us learned to drive in our teen years where emotions may over-ride rationality . . later in life, with slower reaction speed and less overall energy those "bad habits" need to be approached in the overall sense of things wanted & needed. Separating need from want is a workable approach.
She wants to drive a Jeep, fine. She wants to drive a Lexus, fine (she did both along the way). Driving each of them
well called for appealing to the motivation in buying them in the first place as each had strengths and weaknesses while onroad.
Over EPA wasn't hard when done in this manner.
Outstanding description, by the way, of you & your student!!
.