She's definitely appearing in some form by the end of the season

"Following last week's reveal that Holmes (Jonny Lee Miller) had recited her name over and over in his drug-addled past, it seemed more than likely that we'd soon see her in the flesh.

Adler, oftentimes depicted as a love interest for Holmes over the years, will appear before the end of Season 1, Doherty assures us. "Initially we had a back nine [episodes], and now we have a back 11, which is an embarrassment of riches," he says. "So somewhere in this back half of the season we'd like to see her in some way, shape or form.""