I'm going to play devil's advocate for a moment. I used to teach math and science (to high school students, so I understand that it's a slightly different situation.) I used to make them show or explain EVERYTHING, and the reason I started doing that was because of an extremely gifted young man who came through my class one year. He had a talent for Physics, and a lot of the problems came to him almost instinctively. About halfway through the year, though, his grade in the class started dropping. So I started paying closer attention to how he was doing his classwork. As it turned out, this incredibly smart kid was so good at this stuff, he wasn't taking the time to work through the steps - while he was getting the right answer, he didn't fully understand how he got it. It was no problem until the problems started getting a little harder. The class built on itself throughout the year, so not having a thorough understanding of the ins and outs of the problem started to hurt him after a while, when he could no longer breeze through the steps and come up with the answer in his head. So I started having him explain everything to me in minute detail - no more skipping steps. He HATED it at first. But now he is in college at Virginia Military Institute. He recently emailed me to thank me for "making my life miserable," as he put it, because being familiar with that fundamental (although tedious) thought process is making his math and engineering classes MUCH easier for him.
Anyway, my point is that although it seems like a waste, there is actually some logic behind forcing her to explain it. I'm sure it's frustrating for her, but hopefully it will help her in the long run.
