You figure you should at least take a closer look at the desk...

The aisle closest to you has several tall stacks of books, enough for you to get closer to the harpy without entering her line of sight. You creep forward slowly, keeping a close eye on the large creature. She remains oblivious to your presence and continues calmly reading - now that you're closer, you can tell she's writing in the book as well, her script glowing slightly as she does.

Halfway down the aisle, you can get a better look at the strange book as well. Instead of resting on the stand in the case, the book floats ever so slightly. Its deep magenta cover is marked with silvery stars that catch the magically-conjured light filling the room. Whatever it is, the magic it contains is potent. It could even be connected with the succubus...

You glance at the harpy again, considering your options. You are still armed with the Strokmier, and with how focused she is on her reading it's certainly possible to close the distance and banish her. On the other hand, it might be a better idea to create a distraction... there are a few towers of books you could push over, and then examine the case while she sorts them. But you'd have to stay close to the distraction to do that... if you threw a book instead, you could make a noise far enough from you that you'd go unnoticed.

Or... you could just leave like you originally planned.