I've done two .
Both times I was doing 35 in a 30 zone. This appears to be the criteria, which I'm not sure I agree with. It's the people caught doing 40/50 in a 30 zone that need this sort of course too, or maybe a harder hitting one.
The first was a very long time ago (15 years?), when these courses were in their infancy. There was a driving element, which I found very useful.
The second was about 5 years ago, the half day in a classroom course, and while there was some useful reminders, the lack of practical element made it not as useful, and the guy who ran the course, was a dick, quite frankly.
So it's very unlikely that your MIL will have to drive, especially if it's a half day one, and it's likely that she'll pick up a few tips about knowing what the speed limit is (streetlights and lack of 30 signs on side roads being the ones for 'is it a 30' roads.
Also driving in lower gears than it is likely that she was taught to use. Going back a few years, people were taught to get into 4th that being the top gear in most cars) as soon as possible, but now we have much more emphasis on sticking to 30, and possibly different gearing in cars, if your'e in a 30 zone, you should have the car in 3rd gear (and 4th in a 40 zone, and only go into 5th if in a 50 or above).