No, I was thinking from the Watsonian* perspective--leaving aside that she did it because the script told her to, why might Irene choose that as her password? In particular, timing could matter here--when in the course of the episode did she choose it? What did it mean to her when she did it? Etc.

*Incidentally, using the Watsonian/Doylist distinction when writing about actualfax Holmes-derived canons is a smidge more awkward.