Other mistake: In his search of Giselle, when Edward knocks on doors 209 (hissing cat), 405 (barking dog), and 714 (purple guy), the funny thing is that in all three close-ups the three door jambs/trim have the same paint glob markings. The actual doors were changed, but the jamb/trim remained the same for all three shots. (Only visible on widescreen DVD). (01:04:05)
Other mistake: In the song, Happy Working Song, that Giselle sings while cleaning the apartment, she references cleaning the hair clog from the "shower" drain. But in the bathroom scene shortly after, she doesn't know what a "shower" is, so she should not have used that exact term earlier.
Chosen answer: Originally she was scripted to have a few scenes with Nancy, Robert's girlfriend, in the design studio. The Producers deleted some of those scenes. You can see that in the DVD under Deleted scenes, where she has a slightly bigger part and actually has a small conversation with Nancy about Robert's text message apology.