Conservation of detail. It's mentioned because it's important. The first 3 panels are all ridiculous examples of Harley trying to off herself - all within character. The last one is a realistic portrayal of suicide - something that [i/]isn't[/i] in character for Harley. It's supposed to show that this isn't another macabre joke by Harley; it's serious. That means all the details have to be realistic. By not mentioning she's naked artists familiar with Harley would draw her with her suit or some ridiculous costume on, thus turning the serious example of suicide into another joke.Maiev Shadowsong said:Why mention her nudity?
Also, it's possible to depict nudity without making it sexualized. It's called <a HREF=http://tvtropes.org/pmwiki/pmwiki.php/Main/FanDisservice>"Fan Disservice".