Time to go back and listen to Disc 1!
Honestly, this is SO my DS . . . ALL. THE. TIME! I find I have to check his work for every subject almost every day. If he hasn't done the wrong book then he's left out a question or part of the instructions or done print when he was told cursive or gave an answer not worthy of his time, pencil lead and paper it took to do it. He regularly reads beyond the end of the assigned reading, especially if he's only supposed to read part of a chapter (sticky notes are helping mark divisions now). I have learned that unless I clearly set the bar every day for him and monitor then he will automatically do the least work possible.
So, if this is the first time something like that has happened, BE THANKFUL!

And then impose some natural consequences.
Has she listened to all of Disc 1 yet? If not, then just substitute, track for track. It will have the history periods out of whack but she'll just have to remember that as she's listening and realize it's a natural consequence of doing the wrong one and hopefully that will translate into being more careful next time. If she finds it confusing, then maybe you could figure out something different (a few tracks at a time with narrations between on Saturdays or something?).
If she's already somehow done Disc 1 as well then maybe she could listen to the first minute or so of a day's assigned Track (to jog her memory) then narrate what she remembers from the first time.
Or even make her listen again, telling her to come tell you at the end three things she didn't notice/learn the first time she listened. I know from listening to them in August that it would be easy to listen to them multiple times and still learn/remember more each time.
There are lots of options for dealing with it, but I think the most important thing is that she learn from her mistake (even more important than the course material covered) and how to deal with it. It is a very real possibility that something similar could happen again in the future (say, even in college/university) and learning to adapt, make up the course material she missed and facing the consequences will be key skills for dealing with it next time, too.
Oh, and there's lots of time to color in those beautiful drawings yet!

A couple a day seems fair, right?
Blessings,