Motorpacing can be pretty dangerous, so I wouldn't do it unless she has experience as a motorpacing driver. And I would never do it during commuter hours.

But other than that, what CG said. Whether it will be too many miles for you depends entirely on how many miles you're doing now, and if it's much less than your future commute, how hard you want to work to get there, and how much extra time you want to spend on your bike. Remember that it'll be more like two completely separate rides of 33k than like one ride of 66k. After four hours' recovery, your body is pretty fresh again.