Well, it's pretty clear that if the price is lower, more people will buy it.
Unfortunately she is kind of spiking things by telling people "hay guys, if you want cheep books buy mine right now."
The question though is whether you can buy enough to make up the difference in lost revenues. For example, if the book is typically $10, and it's on sale for $2, you need to sell at least 5 times as many copies just to break even.
I'm sure she will sell more, but 5 times more than a typical week?